The Uptown ski chalet

In 1990, when architect Andrew Tesoro bought a 400-square-foot Upper West Side studio atop a Tudor-style building on 78th Street, he dreamed of expanding it into a proper house.

But by the time he’d saved up the funds to do so, city codes prohibited him from moving a key wall of his pad. He also couldn’t add additional full-size floors without violating zoning laws. Tesoro could, however, add a new roof to his 10th-floor abode — and that changed everything.

While the apartment’s roof at the time was flat, he was able to add a 20-foot peaked roof under which he could create 1,000 more square feet of living space. Now Tesoro and his family — including his partner Joe, his 16-year-old son Victor and cats Ruby and Tiny — dwell in a home that resembles a ski chalet.

The ground floor, which has essentially the same footprint as the original studio, houses an open kitchen, dining area and living room. The added roof allowed space for a second floor that contains three bedrooms and two bathrooms, plus a skinny third floor — a sleep/lounge/ storage space — sandwiched between steeply slanted walls.

“It does feel like a little house with a back yard,” Tesoro said. “The ability to step outside is very magical.” The home’s 1,200 square feet of outdoor space has played host to inflatable-pool parties and barbecues.

“Victor had a bar mitzvah here and we had 50 to 60 people,” Tesoro added. Though there aren’t any trees up there right now, his son has been known to climb the water tower in their “backyard.”

“The best part is the view to the east,” Tesoro said. “You see Central Park and the Museum of Natural History.”