Make a website where anyone can make design of cars

I want to make a website where users can design their own cars. They can make whatever design of car they want and every detail of design must be done by users i.e they can design each and every part specifically. User Interface must be so easy so that every individual can design his/her own car without any complexity. They can stretch any part of car they want to and design as they wish. I want my web application to be just like Paint or PhotoShop. Difference is in my web application users will design their cars. I could not understand how it can be done. I want to know the best approach I could use to start my project. It will be a great help!