How I made my own door cards.
1) First, I traced my original door cards onto 1/4" beaverboard (or sheet ABS, 1/4 plywood, etc). If you haven't got any to trace, it might be worth trying to get your hands on a trashed set because you'll need the top metal strip for the front ones. You could realistically draw your own cards and make the metal strip from ~22-24ga sheet metal & a panel flanger. Then, I cut the panel shapes using a circular saw, jig saw & drill. You will use flathead rivets to attach the metal strip to your new door card.
2) I traced the cards onto paper and Builder Board (thick cardboard). I then taped the paper to the wall. I used a mini projector to project an image of the stock panels onto the paper. I adjusted the size until it was a perfect match. I used chalk to kind of sketch out the original lines onto the paper door card. Once that was finished, I cleaned all the lines up using a pen, compass, and ruler to make sure everything was clean and symmetrical (I'm picky that way).
3) I used a sheet of carbon paper to transfer the lines onto the Builder board, again using a measuring stick, French curve & compass (or different-sized jars for different-sized curves). The builder board is used to give your design its texture (high & low areas).
4) Cut your design out of the builder board. Use a straight edge & a snap knife. Be accurate because the vinyl hides NO sins. I left "bridges" to hold the design together so I could trace it onto the new door card then I cut the bridges away. I numbered each piece and each section on the door card so I knew where to lay each piece.
5) Once everything is cut out and ready to go, flip it over and trace it onto another piece of Builder Board for the other door (why do all the fussy stuff twice?!). Then put an even coat of WeldWood Contact cement or WeldWood Landeau top adhesive on the face of the door card and the back side of your Builder Board. Let it tack out for about 10 minutes or so. You have exactly ONE shot at placing the strips in place correctly. The easiest way to place them accurately is to take a long piece of wax paper (like you probably have in your kitchen) and cover the area you don't want the strip to stick to then slowly remove it as you stick the builder board strip in place. The adhesive will not stick to the wax paper so you can place it accurately without worrying about it touching where you don't want it to. Seriously, use the wax paper.
6) When your entire design is glued to the new door card, you're ready for the vinyl! It's kind of more of the same! Evenly glue the back of the vinyl and the front of the builder board and the door card. Be sure to get cement on every surface, including the vertical edges of the design so the vinyl will stick there. If you don't, you won't have sharp, crisp edges. Let it tack out.
7) Lay the vinyl on your table, glue side up, and lightly place the door card face down on it. This is the best way to ensure it's centered. Flip the whole program over so the vinyl is facing you. Using a bone folder (or any firm but not sharp item), start from the center and carefully slide along & press the vinyl into the grooves. You don't want to stick all the high surfaces down then try to "pack" it into the grooves; it'll stretch, warp, and won't stick well. Work from the center out, methodically working the vinyl onto every edge for a crisp, sharp look. If your tool is sticky on the vinyl you can put a dishcloth down between the tool & the vinyl so it slides. Just be mindful not to gouge the vinyl.
8 ) When that's done, you can fold the vinyl over the door card and glue it in place; again, be sure to put adhesive on BOTH surfaces where it's going to stick. Trim out and burnish down and puckers you have around the corners on the back.
Here's my finished product.
I also made a padded insert for above the arm rest. I used gray thread to match the subtle gray accents in my seats. I'm not sure if I'm going to use them though. I can't decide which way I like the panel more. I can add them at any time.
**Just a couple of notes**
This contact cement STINKS!! It REALLY stinks. It makes car paint smell like an air freshener. Wear a respirator and use it in a very well-ventilated area. Normally, I don't pay much attention to that stuff but seriously. Also, the can says there's a risk of a flash fire if you use it in the same room as a pilot light or anything like that. Nasty stuff but it works great and has high heat resistance. WeldWood contact cement also comes in a spray form. It sucks. Don't bother.
Use a disposable brush to apply the glue because it's going right in the trash after. No saving it.
You can do ANY design you want with your panels. That's the real beauty of this technique. I just chose a simple stock look. But I considered this as my insert:
And lastly, good luck with your project! I'm super happy with my panels!
I agree with simple custom patterns. My 2c is that I never like seeing car model names or logos in custom upholstery ie door panels, seat headrests etc. Adding "510" or "Datsun" or "240Z" or "Camaro" or "SS" etc, is redundant to me! But, it is common, as LOTS of people do it 
