Ok, everyone ready to cuss me out for saying this?
Please, search. There are plenty of threads about this. Just to prove it, I typed "body kit" in the search box right above the thread list. It returned 100 threads. Here are the highlights.
do i really need plastic styrene?
This thread talks alot about making body kits. Further, it has imbedded llinks that take you to other good threads like
Ratdat's Wide body 300ZX turbo (late Z31) (please do not reply to that thread).
Here is a thread that g00ey started asking for the same answers.
Then I searched "bodykit," one word this time.
ground effects? is the same question, again, but this thread has a great little sketch by our resident body kit manufacturer explaining how to do it. Fantastic!
Look, another thread
here by GTRRR. Neat!
Feel free to search more, I didn't look at much more than the first page on each of those two searches. Try "Body kit, bodykit, body kits, bodykits, ground effects, custom bumper," and so on. I'm sure you'll find more information than you could possibly read.
Welcome to AF, the forum is a great tool. You can learn alot by reading what people say and what people have said in the past. I can't wait to see what you can do!