Rooftops turn out to be extreme real estate, housing both the poorest and the richest. In Hong Kong, Cheng Chung Au and his wife live in an illegally built cage flat on top of a high-rise, coping with rats and typhoon winds because they can't afford a regular apartment and the social housing waiting list stretches for years. The film crosses to New York City, where rooftops once held cramped servants' quarters before developers converted the same spaces into penthouses and bars that now sell for hundreds of millions of dollars. Archival plans for Rockefeller Center's abandoned 1920s rooftop garden and public bridge network show how close the city came to a very different skyline. Activist Anastasia Cole Plakias appears at Brooklyn Grange, one of the largest rooftop farms in the US, explaining how greened roofs cut sewer overflow and reduce heating and cooling costs. New rules requiring green roofs or solar panels on new construction close out the film's case that rooftops are becoming a testing ground for the future of cities.