I agree with 2 or more doors. No matter how much light you put in the building, when you back in, it's hard to see. Here at work, Ed always has me guide him as he backs our car-hauler trailer in, and that part of the building is brightly lit.
Regarding door types: on our old pole barn, we had a sliding door because it gave us a few extra inches of height (12' walls). Here at work, we have 12' wide x 14' high insulated overhead doors opened by commercial openers. The biggest drawback is that if we ever lose power, I'm not sure we could open the massive door by hand?
