We spend much of our days with a roof over our heads, but rarely think of how roof exteriors could be so much more than just a weather shield. The growing urban rooftop farming movement just may change that. An article in today's New York Times describes how the green roof movement and the healthy food movement are converging. City policies can play a role in acclerating plantings - Chicago and New York provide tax incentives - though the urban farmers surveyed in the article admit rooftop gardening is more a labor of love. Although they can be expensive (even if subsidized) and not suitable for every type of roof, green roofs also provide public benefits through reducing urban heat island effects, cleaning air, and producing local food. For a vertical spin on growing food and plants in an urban setting, check out the blog Veg.itecture.