Designing a car is pretty hard since you need to know a lot of knowledge regarding CAD applications or 3D design software related applications. Designing a car should start with a blueprint in case you want to use software like 3DS Max which is able to do all the modeling, designing and rendering. Another solution would be Catia which allows for complete modeling of objects or parts and not only. The approach to the problem is entirely yours depending on your knowledge regarding CAD or 3D modeling applications.
