If you plan on using those cans they sell at the auto parts store, that's made especially for exterior applications you will be spending a lot of money. I used a can on my work truck on the hood and was only able to apply 2 coats on one side of the hood and it still needed about another 10 to really look like it did something. Your better off vinyl wrapping your car with a paint brush for only like $350.
http://www.youtube.com/watch?v=kiQntbVmTp0