Growing food on a rooftop can be as simple as putting a few homemade self-watering planters or Earthboxes around the perimeter of your roof, or as advanced as creating an intensive green roof with a mixture of vegetables and grasses.

http://www.artic.edu/webspaces/greeninitiatives/greenroofs/images/GuidetoRooftopGardening_v2.pdf

http://www.thekitchn.com/how-to-make-a-green-rooftop-ga-51257

http://www.tremcoroofing.com/

http://www.greengridroofs.com/

http://www.earthbox.com/

self-watering container

http://www.theurbancanopy.org/