First off I know that this has already been covered here: but in my opinion it wasn't detailed enough. Since I'm already essentially doing a diy for this for my senior project might as well toss this on here as well.

Here is a list of all the materials I used for this diy (I'll keep updating this as I purchase more supplies):
Hood - $53 from junk yard
2" x 4' x 8' foam sheet - $33.25 from Lowes
kobalt 2-peice keyhole saw - $5.98 from Lowes
razor knife - $1.69 from a local store
20" x 32" mat board - $3.00 from a local store
2 paintbrushes - $1 for both from Harbor Freight
Riveter - $5.99 from Harbor Freight
Assorted Sandpaper - $4.29 from True Value Hardware
Gorilla Glue - $4.99 from Wegmans
Body filler - $9.69 from Surplus City
Fiberglass mat - $7.89 from Surplus City
One Quart of Fiberglass Resin (Bondo) - $22.39 from Surplus City
Spreaders, mixing cups, mixing sticks (could be whatever you can find), got mine from Surplus City for $2.16 total
Spray foam (Great Stuff) - $4.27 from Wal-Mart
Double stick tape (Locktite) - $6.97 from Wal-Mart
Modeling Clay - $2.64

And here's the design and dimensions: (the lights are 2.6" thick)

First thing to do is make your design. I used AutoCAD to make the initial from template and then switched to Solidworks to make the 3D Model. You don't have to do this step but making a template on the computer is more symmetrical. You can get Draftsite for free to design your template, the link is provided under this paragraph along with a link for 2 designs I came up wit. First take measurements of where you'll be mounting it prior to designing it. I'll include the dimensions of mine as well as the dimensions of the lights for you guys later. If you wanna do it all by hand go for it but you'll need a compass and ruler.

I'll be checking my design on a second and third gen leggy tomorrow to see how it looks. If you're going the "print off computer" way than here's how you can print it from draftsite:
Click File
Select your printer
Uncheck the "fit to paper" box

Set the scale to 1:1

Click "specify"

I have these separated into 6 quadrants, those green boxes are the size of a typical sheet of printer paper. Window one and print it. Repeat this for the other 5 quadrants. (sorry there's no other way to do this that I know of)

If you want to change between the print quadrants, the drawing, and the dimensions here's how you do it:
Click the window circled in blue

The 3 selections windowed in red are the ones you need

If the little circle circled in red is white than the selection is invisible, if it's green it's visible

And when you bondo you don't need much hardener. This shows a good relationship of hardener to bondo.

If you design it on the computer print it off. You may have to do multiple prints and put them together, which is what I did. If your drawing it by hand then draw it directly on the mat board. Mat board is basically a thick sheet of paper. My board was 1/8" thick but construction paper or carboard will do the trick as well. If you printed it then tape it to the board. Cut the board around your design and this will be your template.

Once you have it all cut out place your template on the foam sheet and cut just outside of your template, about an inch or two. Once it's cut out put your template on the cut out foam and trace the design. I traced it with the razor but you could also use a sharpie. Once finished you could start cutting the design out of the foam. I found it easy to cut a bunch of straight lines taking off small chunks and lightly touching the traced line. Once it's all cut down then I used 36 grit sandpaper to take off all the rough edges and used 100 grit to get it kind of smooth.

Here's where I have to explain something. My project is to make a mold for this and thermoform the parts. To make this happen I have to make it in 2 sections but other than that it's essentially the same. I gave 2.75" from the front of the housing to where it begins to taper. Since the foam is 2" thick this will be tricky. You could cut out another sheet of foam using the template and cut out an outline. I did this by first cutting the foam in half to make it 1" thick. This is a severe pain but basically just measure 1" all the way around the thickness. Cut down pretty far with your razor knife and then cut out pieces with a bunch of straight cuts and use all the outside pieces. You might wanna label what goes where to make this easier.

Elmers glue worked ok but due to sanding and all I went a little higher strength. Got Gorilla glue from Wegmans which works pretty nice. I also ditched the multiple outside pieces and cut the outside outline off of the other 1/2 of the foam. The foam in the pic is 1" thick from when I cut it in half. I didnt get a pic of it seated but will snap a pic after the glue dries.

Once the glue is dried the two pieces will most likely not match up perfectly, sand the sides down to make them straight.

Polyester fiberglass resin will eat the foam so you need a shielding layer. The other diy used packaging tape which seems to be a pain if you get any wrinkles. I originally tried plaster which worked but chipped a little too easy on corners so bondo it is. The bondo eats the foam a little bit but I plan to use 2-3 layers of bondo to counteract this. Again, if you're doing one light pod then you can make this all in one piece rather than in 2 like I am. If you want to make a mold to produce a couple then do it in 2 pieces.

I started on the other half today. I cut all the pieces needed to do the other half. Next I'll be getting the foam to contour to the hood and then shape it.

I tried to mount the foam pieces to the hood using awesome double sided tape but it wouldn't stick. It stuck two pieces of foam together pretty nice but when I wanted to stick it to the hood it didn't wanna cooperate, I don't know what happened so I scrapped that idea. Instead I put a layer of fiberglass on the hood and will glue the foam to the fiberglass with gorilla glue. Then I'll fill in the voids with expandable foam, sand it all down, apply bondo, sand some more, and mate it up with the first half. Once finished I'll then put fiberglass across both halves at the same time and then cut them apart so they match up perfectly. After that I'll remove the fiberglass from the foam and duct tape the two halves together. Then I'll wax the back half of the mold and add a fiberglass lip/guide to the front half. I haven't done this yet as I am waiting for the fiberglass to cure. Also, I know in the pic I didn't put resin on the entire sheet of fiberglass. This is because I will be cutting it to the edge of the foam so when I put the top layer on it will allow the fiberglass mold to contour to the hood itself rather than having a space.

I used locktite double stick tape to attach the first (front) sheet of foam to the hood and used some spray expandable foam to help hold it at the angle I wanted and also help keep it to the fiberglass. I then cut the contour of the hood into the other layers of foam and added them one by one to the hood using double stick tape on the bottom and in between each layer. I also used gorilla glue in between each layer and on the last layer put some expandable foam in between the layers just to see what happens. I put more expandable foam under the foam layers to build strength so I don't accidently crush it. (I cut the centers higher up so I didn't have to contour the entire layer to the hood, just two small feet.

From here sand down the foam in an arch or whatever shape you please. Then add bondo and sand it smooth. I'll have to contour mine specifically to the first half so it all matches up perfect but if you're doing a one piece then it should already be attached and sand it all together.

I found that it was easier to use the spray foam can and sandpaper to get the curves between each light housing

Apply bondo and sand smooth, and if there's any holes than you could use spot putty and sand it smooth again

And I did some testing. Once bondowork is finished and smooth than add some paint, well a lot of paint. This way you can wax the mold to apply the fiberglass. I did a test and duplicolor paint works well. Did two heavy coats and it came out nice. The only reason there's scratches is because I didn't feel like sanding it was sanded with 40 grit sandpaper very poorly.

If you are doing two parts like me, cut out the bottom portion of the front half enough to clear the hood. You might not need this step depending on where you put the other half on the hood. Also, again with the 2 part mold. You could attach the two halves with gorilla glue and spot putty (since the glue sets in 1-2 hours and the spot putty sets in 20 minutes). Painters tape and excess foam can help hold it together.

After they're together, get the edges as close to the same as possible and you could bondo the rest to make it flow together.

Sand it all down nice and smooth. Again, I used 40 grit and 100 grit to do the job. Make sure all holes are filled and smooth.

Once everything is smooth and even you can now pop the fiberglass with the mold off of the hood. This is where you learn if you waxed good or not. My roomate and myself used a putty knife, scrapers, and eventually 65 lbs fishing line and sawed back and forth to separate fiberglass from hood. WARNING: Do NOT even think about using resin from surplus city. I used it for half of the fiberglass and it ate through the paint, took over 2 weeks to fully cure, and was hard as hell to remove.

Cut the excess fiberglass away from the mold. You could use anything from razorknives to hacksaws. I used a dremel with a cut off wheel and it took no time at all.

Unfortunately I don't have any pics of the next step. Put bondo around the edge going from the mold to the fiberglass (I didn't want to cut too close) and then sand it smooth. This makes a nicer transition to the hood and lowers the risk of cutting into the mold by accident. Go over the mold and make sure it is all perfect to your liking. Once finished sand it with 220 grit sandpaper to make it extra smooth.

Place the finished mold back on the hood and sit behind the hood while making car noises and act like a child.

Once your imaginary rally is finished and you placed first, start painting the mold. I don't know how well bondo itself waxes but paint will make the mold look nicer anyway. Start with a slight spray for the first coat, once dried add heavier coats. I have one light coat and 2 heavy coats on mine. One small can of duplicolor paint did the entire mold for each coat totalling 3 cans used so far.

Once completed wax the mold and the hood. Place double stick tape on the bottom of the mold and place it on the hood. Go around the perimeter of the mold where it meets the hood, chances are there will be a gap, jam clay in there and use a razor blade to make it flat.

Now wax everything again and then apply the fiberglass. Some areas you'll need to cut slits in to help it contour to the shape. If you're only making one than this will be your part. Use a paintbrush to apply the resin and basically stab the air bubbles out. Make sure you saturate the fiberglass over the hood about 2 inches for a flange. Apply at least 3 layers of fiberglass and make sure you have enough resin before you start. I ran out when I was almost done and had to run for more, causing 2 imperfections that I had to try and work out and hope it works. I used one layer for flexibility to help get it separated from the mold.
When I did my test piece I noticed that the paint came off with the fiberglass but it scraped off really easy.

After the resin has cured you can remove the fiberglass from the mold. If you're only making one than use any means necessary to remove the foam. You can use acetone to reduce the foam. It doesn't eat the polystyrene but pops all the bubbles that are in the foam. Then you can scoop it out. You could also try to "pop" it off the mold by using putty knives to separate the fiberglass from the mold. I had to cut through the fiberglass where the two halves of the mold were assembled and also where the lights will be cut out. Then used a butter knife (which broke) and a putty knife to start popping the fiberglass from the mold. You can also hit the fiberglass with a hammer; this will shock the pieces apart. You can tell what's popped by the paint color not showing through the fiberglass.

I kinda sorta failed to wax it good enough so let this be a lesson to you all who attempt this. Wax wax wax and if you have doubts of it not being good enough wax it agian.

Notice the paint that pulled off with the fiberglass. This easily scraped off with a straight razor and a scraper. It's still a little bit red but it won't affect anything.

Duct tape the two halves back together and wax the side you don't want the aligning flange on. Then apply the fiberglass to create the flange. You'll notice I always leave some unsaturated fiberglass, it's just what I do and it makes it a little easier to remove.

Test fitting before I got the chance to trim

Trim the flange to your liking, drill the mounting holes, cut out holes for the foglights, and finish it up. (Mine's not cut out for casting purposes.

And that brings this project up to where I currently am at.