Living in a high rise, yet not on a rooftop, I tend to look out of the windows a lot. Since a couple of month I have noted a definite change in the city. From my vantage point I spotted at least four buildings where an extra apartment is added on the roof. If they aren't creating new living quarters, people have turned their roof into an urban garden or have installed solar panels.
Here, on the left, you see a new apartment under construction and behind it on the slanted tiled roof, new solar panels. The small dark gray corner top apartment is brand new and is offered to students as a good place to stay. This tells me that in an urban setting people will create gardens, green refuges or overflowing balconies where ever they can and also that the price of land is so exorbitant that it is cheaper to just add an extra floor. Interesting what one sees from a it higher up.