In Newsweek, there is a good article about green architecture in China (project summary here). US architect William McDonough plans (among other things) to:
The cities are zoned for mixed residential, commercial and industrial use to ensure that transportation connects residences to the workplaces. Shops will be on the ground floor, residences above, and the rooftops will have farm plots. Bridges over the streets will connect the plots. The farmers will live downstairs. (...) McDonough's ideas have worked well, albeit on a smaller scale, in the United States. He's designed green developments for communities and corporations, including the Gap and Ford. The headquarters for the clothing retailer the Gap in California has a roof with vegetation on it, a raised floor for better heating and cooling, and makes good use of daylight.
Why do I blog this? I like this idea of roof farms; besides my parents' house is made of a vegetal-roof (no tiles), maybe that's why this idea is not so weird for me.