Still, in a city made up mostly of rentals, there are exceptions to every rule. Kurt Franz, 30, a project manager for a Brooklyn-based real estate developer, created a fifth bedroom in his previous apartment, a TriBeCa loft that he shared with four roommates. He also built a large floating dining table by bolting a large slab of wood to a pillar in the kitchen. When the lease was up and the group decided to move, the roommates asked the landlord if the floating table and the fifth bedroom needed to be removed. The answer was no, Mr. Franz said. Instead, the landlord refunded their deposit and increased the rent for the next tenants.

Mr. Franz got even more creative at his current abode, a fourth-floor walk-up in the East Village that he found with the help of his former roommate, David J. Bucci, a real estate agent with Coldwell Banker AC Lawrence. The “shoe box” apartment measures about 360 square feet, said Mr. Franz, who moved in about a year and a half ago and pays $2,200 a month. To maximize space, he built storage benches and a Murphy bed. He extended the wall in the bedroom to create a big screen for a movie projector he hung above the bed. In the kitchen, he built an elevated dining banquette that doubles as a cot, and a table with a built-in flat-screen TV that pivots up when the cot is needed. Oh, and there is a small built-in keg.

It doesn’t hurt that Mr. Franz, who works in renovations, has a history of furniture design and repair. He estimated that he spent only $1,500 on materials, but it took roughly eight months of working each weekend to complete the project. The custom-made space, he said, is worth the effort. “After a chaotic day,” he said, “when you come back to something that’s really tailored to you — I just enjoy it.”

His landlord has yet to learn about the modifications, but Mr. Franz does not expect any issues, especially since he was careful to make his changes and additions easy to remove. “Everything is built-in and customized to the space,” he said, “but in actuality there are probably 12 screws in the wall.”

For some landlords, timing is important. One, Alan Dixon, an investor from Australia with a growing portfolio of more than 530 rental properties in New York City and Hudson County in New Jersey, said he was willing to incorporate renovation suggestions if prospective tenants made them before he began a project. He said he had done so about 10 times in the past 18 months, in properties like a two-bedroom in Jersey City that he ended up renting for $1,300 a month, and a Brooklyn townhouse that he then rented for $12,000 a month.

Last year in Jersey City, after he acquired a four-story brick rowhouse that he planned to gut-renovate and rent for $7,690 a month, a couple with two small children expressed interest in renting the place. He asked them for a “wish list” of things they would like done to the property. As the renovation progressed, he incorporated their suggestions, among them revamping the garden-floor layout with an open kitchen, relocating the laundry room, and opening the garage to the backyard.