A few months after selling for $13.5 million, a Brooklyn Heights apartment building is being marketed as a single-family home at nearly twice the price.

Benchmark Real Estate Group, a Manhattan-based real-estate-investment firm that bought the 20-unit rental building in January, is putting it on the market for $22 million, according to listing agent Ryan Serhant of Nest Seekers International. While some tenants are still in place, the roughly 14,500-square-foot building will be delivered vacant, he said.

Benchmark hired Lee Stahl, of design/build firm the Renovated Home, to draw up plans to convert the building into a single-family home with four bedrooms, a gym, a wine cellar and a roof terrace. Mr. Serhant said a buyer would be free to use those plans—and work with the Renovated Home on the project—or not.

“Every buyer is going to want to do it their own way,” Mr. Serhant said.

The idea, Mr. Stahl said, is to help the buyer envision what the redesigned home could look like and how much it would cost. Mr. Stahl said executing his plan would cost about $10.6 million and take 16 months to complete.