National Geographic: The rooftop of Robert Green’s home bears two unmistakable marks that it is part of the effort to rebuild New Orleans with a new resilience. There is a safe exit to a secure area of the roof–a feature that needs no explanation for longtime Lower Ninth Ward residents like Green, who lost both his mother and his three-year-old granddaughter in 20-foot-high floodwaters after the Industrial Canal levee broke in the wake of Hurricane Katrina on August 29, 2005. But in addition to …