As roommate chemistry goes, it’s hard to find a better pair than Caitlin Sikora and Chelsea Retzloff. When the two friends, who are in their early 30s, met through a dance workshop five years ago, they learned that Ms. Sikora had degrees in dance and physics, and Ms. Retzloff had degrees in dance and … chemistry. More recently, both wanted an upgrade from their rundown apartments.

Ms. Sikora was renting a small one-bedroom in the Chinatown neighborhood of Manhattan for around $2,500 a month. It was covered with layers of paint and plagued with construction noise. The water tasted metallic. After her roommate moved out, she lived there alone.

“I didn’t think the space would work well with the wrong roommate,” said Ms. Sikora, who works as an engineer at Google. “It was too expensive for one person and too small for two people.” She wanted to lower her rent to help pay down her student loans.

Ms. Retzloff was living with three roommates in a walk-up above a loud bar in Park Slope, Brooklyn. Her 7-by-12-foot room had a lofted bed she had built from galvanized steel pipe.