Building on a new hanging garden trend, a greenhouse atop a Montreal warehouse has set a record as the largest in the world. Growing eggplants and tomatoes to meet demand for locally sourced foods, the Lufa Farms facility spans 160,000 feet -- about the size of three football fields. “The company’s mission is to grow food where people live and in a sustainable way,” said spokesman Thibault Sorret. Since Lufa Farms started building rooftop greenhouses in 2011, competitors have picked up and run with the idea, building rooftop gardens in New York, Chicago and Denver. Lufa Farms's rooftop gardens “recover energy from the bottom of the building,” allowing savings on heat. They're also very water efficient.