This issue recently came up - when buying a house, condo, etc. with an empty space of land next to it, does the guy who owns the ajacent land have the right to block your windows?
Simple answer - he can build whatever he wants on his land. So anyone can block your windows - you don't have the right to light, air, etc. Pretty scary.
P.S. to the best of my knowledge, there are no zoning laws against blocking neighbors' windows.