Sky Vegetables
is an interesting Blog/ Website on Urban Rooftop Farming: http://www.skyvegetables.com/

Here are a few stories from them.

Plastic Wading Pools + Roof = Successful Vegetable Farm
April 4th, 2008

Dr. Ebenezer proved that growing vegetables on a rooftop using plastic wading pools was feasible. In 1997, Dr. Ebenezer and his team were able to harvest 984 pounds of vegetables from 38 pools in an area measuring 1,625 square feet. One pool alone yielded an average of 22.5 pounds of tomatoes, cucumbers, bell peppers, zucchini and a variety of greens. This is equivalent to about 26,800 pounds per acre. This is a photo of Dr. Ebenezer with his wading pools

By: Geoff Wilson

Gregory Chow has demonstrated already, what can be done in rooftop farming with his award-winning project on the atrium of the 800-bed Changi General Hospital The hydroponic farm on the atrium of the 800-bed Changi General Hospital in Singapore. The bare concrete of the atrium roof was a problem in that it diverted sunlight into nearby wards - to cause objectionable glare and heating. The rooftop hydroponics, growing cherry tomatoes and herbs, solved the problem and created a rooftop farm that now supplies patients with healthy fresh food. Another Singapore hospital is about to go even further in food from the roof.