Three-story homes, at least of the detached, single-family kind, are not that common. At most new developments the designs are limited to one- and two-story homes with shoulder-to-shoulder lots.

the Upper West Side. Ms. Eggertsen had been the first to move to the city, three years ago, paying $1,800 a month for half of a converted one-bedroom in Stuyvesant Town. “I was far from the ...