The invention discloses multi-storey building structures of different sizes and purposes, built on long-span beams laid on cornerstones of minimal dimensions, on the opposite sidewalks of streets and the medians separating street lanes. Such buildings basically occupy the air-space above streets and roads and may be used for parking garages, residential, office and commercial space or for an optimal combination of them. Parking garages built on the air-space above intersections of roads may enable entry from any direction and exit to a different one, with or without parking and greatly contribute to the rationalization of car traffic in modern mega-cities. Such multi-storey buildings comprising in addition to parking garages, office, residential and commercial space, may save valuable timing wasted in going from one place to another.