New York magazine's editors asked four architects to come up with plans for the empty plot on Canal and Varick that faces their office. It's no surprise that one of the submissions was green-themed. (The surprise would be if one of them wasn't.)

Green roofs are lovely—an oasis to keep city dwellers sane while improving the air a little too. But a farm on the roof? More specifically, cut across ascending tiers? “We are interested in urban farming and the notion of trying to make our cities more sustainable by cutting the miles [food travels],” says WorkAC co-principal Amale Andraos. But sustainability involves more than just cutting down on the miles that food travels. Much as we hate to admit it, it involves economics.

How much would such a building cost? What about the roof itself, keeping in mind that such a roof requires not only a dirt substrate, but also filter fabric, drainage, protection layer, waterproofing, moisture barrier, and insulation. Who will till the land and how much will it cost to irrigate? How much will they charge, one year later, for one Red Delicious? (Plus $5 for the novelty, plus $2 for its being organic?) Never mind that the apple tree stews all day in urban exhaust. Never mind that it tastes like the muffler of a yellowcab. Discount if it's fresh off the tree—that is, if it falls off floor fourteen and hits you in the head. No coupons necessary. Just bring your battle wound.

--Francesca Mari