[TeMPOraL]

I think flying within centimeter distance of a building could present some additional technical and safety challenge (wind, avoiding people getting their fingers sawed off by rotor blades), but the legal hurdles will the biggest problem, I think.

There is little safe space to fly over in cities - you can't just start flying over roads and pavements, because if any malfunction happens, you'll be dropping a 10kg high-velocity brick at people and cars. You'll need at least specialized insurance for that, and I'm not sure if anyone gives this kind of thing.