Flying taxis are obviously a pipe dream, right? Wrong, apparently. A series of prototypes has started surfacing in recent months, such as from German start-up, Lilium, with promised commercial delivery horizons of about 5 years. Such is the sincerity around delivery that the regulators are starting in earnest to certify operators, reports the FT this week. Setting the rules won’t be easy, especially with flights over dense urban areas. However, an equal challenge is how our built environment would cope with an increase in vertical take-off air traffic. For instance, in the UK’s biggest city, London, there is only one centrally located heliport (at Battersea). Parks and other large green spaces might provide opportunities to site landing pads. However, whilst 47% of London has some form of green coverage, most of that is in outer areas or private gardens, leaving less than 20% as Public Open Space. Another option is the Thames. If Boris could build a new global airport in the estuary, presumably a few helipads in the central section should be an easy matter? These would have the advantage of being located close to nodes of expected demand. Finally, we have rooftops. Traditionally a home for plant, and now increasingly the best bit of the building to deliver bars and restaurants (our report here), roofs could in the coming years find new demand as an access point for both passengers and drone deliveries. Particularly as our cities densify and ground floor infrastructure becomes stretched, the interesting bit of the office tower might move from the bottom to the top.