What alt are you overflying, and where is your distance slider set to?
Take a look at this video...you can see when the buildings are "rendered" into view.
So normally you use geographical references to help you locate stuff in the air...by this I mean roads, the center strip, etc...and then as you get closer you "break out" the building you want. Big to small---walk yourself in. Having a map of the base helps, because then you can count roads, etc... to get your desired tgt building.