Have you ever been inside a tall building? How are you thinking a drone would deliver to the upper floors of vertical buildings? The windows don’t open. There are occasional balconies or terraces, but these are more the exception than the rule, especially for “hungry office workers in a Shenzhen skyscraper.”
Residential buildings usually have operable windows (and often balconies). My condo building is only 17 stories tall, but my windows open all the way. On the other hand, it's an old building and there might be new rules for new buildings, since for those I usually only see the windows open a little.
Still it would be silly to deliver through the window. The rooftop might make more sense (can just drop off package and not accessible to random people on the street).
