I usually buy carbon sheets from CST (http://www.cstsales.com/index.html) and make my chassis out of it when I am doing prototyping or custom applications. It is expensive but comes out light and strong, but the first step is to make the desired template out of a piece of cheap aluminum or tin then transfer it to the carbon once you have all your placements and everything the way you want it where you don't waist the expensive carbon with mistakes, you can even make your prototype first out of a fiberglass sheet then take it to the stronger carbon.