will depend on mostly if you do need a lift or not.. Most lifts need 12'2 to like 12'4" range... That is plenty high for a car but for a pick up you might want 14' ceilings..
What size and type vehicles are you planning on storing both under and above? I am in the process of looking for one too and I have seen the outside widths go from around 100-125 inches.. So if it is a smaller car I would prefer something that does not take up extra garage space.