I can't think of a single building that wouldn't have roof access.

My house. My neighbors houses. Old stone churches. Airplane hangars. Boathouses. Small to Medium sized apartment complexes. Small to Medium sized retirement homes. Small banks. And lots of other places.

Yeah a lot of those places have sloped roofs, but saying that you really only need to worry about sloped roofs is like saying you really only need to worry about the water if you're afraid of drowning. Or maybe it's different where you live. But around here, most roofs, the most by far, are sloped or otherwise inaccessible without serious effort. And most of them aren't so sloped, that the a drone would reliably slide down, and that's not even to mention lips, gutters, corners, large tiles, and other hindrances. If I got a drone stuck on top of the church across the street from where I used to live, I would not be getting it back. No access without an industrial ladder, and no way they would let me knock about on their roof.