No they don't; they buy in a chassis/body combination and also the engines, and put together what is a Porsche but with additional or supplementary RUF parts. They don't design the car at all, but use Porsche models as a basis. Their own website tells you this (not having heard of them, I looked them up). As said, it's just like AMG who take a base Mercedes chassis/body and add their own bits. I'm very impressed with some of their performance claims, however; these things must be very, very light indeed.