This massive rooftop garden being built in Brooklyn, NY will be able to produce up to 1 million pounds of food per year.
http://www.urbanfarmonline.com/urban-farm-news/2012/07/06/worlds-largest-rooftop-garden.aspx
This is a companion discussion topic for the original entry at https://peakprosperity.com/worlds-largest-rooftop-garden/