I love the building in the photo, with the saffron walls, and the balconies.  It looks VERY expensive.  It does NOT look very New-York-ish, though.

And the greenery looks decorative, not gardeny.

Keeping plants on upper levels is always tricky, because of the water supply problem, as well as the water leakage problem.  (Thanks to Umbra and Laura, though, for bringing attention to the problem of potential air pollution, which would not have occurred to me.)

If Laura, living in NYC, has her own roof with her own private garden, good for her.  For most of us in NYC, though, that is not possible.  Roof gardens would have to be common projects in coop buildings such as mine.  Plans and precedents for that sort of thing would be welcome.