hey man, i dunno much about making bodykits, but i have made a few things from fibreglass (subwoofer/speaker installs). youve just gota somehow come up with a mould of some sort, maybe use wood/chicken wire/....i have no idea how you would make a mould for a body kit, but im sure its doable somehow. and then you just cover the outside with heaps of layers of fibreglass, and then rip out the mould and technically you should have a nice looking shell left. im sure it would need a fair bit of bog/sanding to make it look decent, but its prolly doable.
i was thinking of making a little "lip" for the front of my ke70 out of fibreglass, see how i go with that....
hope this helps
-David