There are about a thousand real-estate developers in New York City. Nathan Berman is one of them, and he’s become rich doing it. But, he told me recently, “I never built a building from scratch, and never wanted to.” Instead, Berman, who is sixty-four, specializes in taking existing structures and converting them into apartments, a useful trick in a city that’s always starved for housing—and newly wary of the five-day-a-week office routine. In 2017, he converted 443 Greenwich Street, a former wa...