“If things are looking up for architecture in the 21st century, it’s partly because of the roof. After decades of neglect, it is once again becoming the most visible element of new buildings, let alone whole cities. All those flat-roofed towers constructed since the 1950s and ’60s are being reimagined as occasions for greenery, gardens, pools, playgrounds and even parks. Then there’s the advent of Google Earth, a free computer program that has people everywhere looking at buildings — and entire cities — from the top down. Suddenly, the whole planet has been turned into a roofscape.”