I read that article, too, and wanted to link it in my OP but couldn't find it. And yet, they're doing it in Milan, not just putting it on drawings. I'm not arguing against the scientific reasons that putting trees up on TOP of a 600 ft building (however, tree lines on mountains can be anywhere from 500 ft to 6,000 ft). But 18 to 24 story buildings like these with trees on ledges (much more shielded from wind, accessible to water) are feasible. Depending on the global location, on top of the roof isn't that outrageous, either:
http://www.mimoa.eu/images/1200_l.jpg
http://upload.wikimedia.org/wikipedia/c ... ologio.jpg
http://activerain.com/blogsview/3149723 ... -the-tree-
http://www.archdaily.com/348582/hotel-a ... irudavolu/
http://www.flickr.com/photos/linkef/3657807532/
Even if it's not fully blown 'trees' small to mid-rise buildings could have smaller shrubs, bushes, grass, landscaping, etc to help reduce heating/cooling costs, water runoff, etc. It has been done (I can't find an image of the Singapore building I'm referencing but it was easily 30 stories with full grass/trees on it) and even if the skyscraper images are aspirational they may drive behavior on the mid-rise stuff.