Rooftops for commercial use, rather than EMS, have a bad smell about them. The Pan Am crash did most of that. There are issues with finding a rooftop that isn't already occupied by air con coolers, cell phone towers, microwave repeaters etc. Then you need to have the rooftop certified as strong enough to land machines of certain size there, fire protection, bunds for fuel leaks, pax protection from being blown away, waiting areas, staff to supervise load/unload, access for pax through somebody else's building, insurance, blah and blah.
Generally falls into the "Way too hard" basket.