When I built my home, I built it with an 11' high garage ceiling. I thought that would be enough for anything that I might consider lifting. Now, my collector cars have changed and they are much higher than the Corvairs that I owned when I built my garage. I could use a 14 or 16 foot ceiling to accomplish what you are thinking about with your cars. Just keep in mind that you can never have too much room. If at all possible, go for the highest building that you can reasonably afford, in both length, width, and hight. Your choices of cars can and will change, but once built, it is very difficult to change the building. Also, keep in mind that in the building trades, measurements are on the outside, so if the building is 24' x 32', you are going to loose between 8 - 12" of space due to the thickness of the walls. Measure the length of your car, and see how comfortable you are with the space that is left over. My garage is 38' deep which gives me 37' on the inside. If I had an additional 4' inside, it would double the amount of cars that I could get into the garage. Something that I didn't think about 25 years ago when I built it with Corvairs in mind.