David H Rosen, a lifelong New Yorker, left the city for only four years, to attend Cornell University in Ithaca. After returning for a Ph.D. in psychology at New York University, he scored a rent-stabilized two-bedroom in Prospect Heights, Brooklyn. He brought in the occasional roommate, but mostly kept the place for himself and a cat or two.

Always interested in buying, Mr. Rosen checked out plenty of apartments over the years, often in small walk-up buildings. One place in Park Slope was a two-bedroom with a roof terrace and an attic.

“It was a standard beautiful brownstone — old on the outside, new on the inside,” Mr. Rosen said. A spiral staircase led to the tiny attic, with skylights.

“I thought that was the coolest thing, this attic,” he said. “I couldn’t afford it at the time, but every place I went into, I compared it to that in my brain.”