Just outside of Philadelphia in one of the Main Line’s ritziest areas, the famous architect Horace Trumbauer designed and built Green Farms Hotel in 1919. It was meant for wealthy day-tripping Philadelphians, the type of place where Gatsby would’ve gone when he blew up at Tom Buchanan in the Baz Luhrmann movie version of “The Great Gatsby.” Then in the late 30s, post-Depression, Eastern Baptist Theological Seminary bought the property, and for around 70 years prospective religious members learned about the church and lived in simple dorm rooms there.

Now it’s a place where Philadelphians can live. It opens as the Palmer, a new apartment complex this spring.

Our city brims with apartments, condos and lofts like the Palmer, places that used to be something else, be it a church, factory, high-end jewelry shop or historic office building. With tons of old buildings that have gone unused or neglected and cheap prices for developers creating optimal conditions, these — we’ll call them funky apartment complexes — have been getting built throughout Center City, Northern Liberties, Fishtown and beyond. Here are a few:

Memphis Flats condos: A former factory in Fishtown

Iron Mill Lofts: A former Iron Works factory in Northern Liberties

1530 Chestnut: Once the Bailey, Banks and Biddle Building where high-end jewelry was sold

Lofts 640: A former factory in North Philadelphia, it was called the Mulford Building and famous for producing the diphtheria serum transported all the way to Nome, Alaska. The Iditarod dog-sled race now commemorates the final leg of that trip.

ICON: Former office building in Center City whose tenants included shipping companies

Oxford Mills: Once a dye works factory in South Kensington.

Kevin Michals is the principal of Cross Properties, the real estate development team behind the Palmer, 1530 Chestnut, the Icon and other similar projects. Beyond Philadelphia’s quantity of old buildings, he said tax credits and comparatively low rental prices are bigger reasons why old buildings become apartments.

Cross Properties regularly applies for historic status for its redevelopment projects so they can get tax credits that have saved the company anywhere from $5 million to $18 million depending on the size of the project. To get the tax credit, a developer must keep the building intact, including any pieces of the interior that are historic or really cool, like marble floors or walls. That’s why developers don’t always tear down Philadelphia’s many old buildings.

A developer also has to exceed the amount he spends on the property fixing up the property to get the tax credit. In Philadelphia, with selling prices at $100 or $200 a square foot for these buildings, redevelopment is a much better investment, meaning places like those you see above can actually happen here.

“In New York City you can’t buy $100 a square foot,” Michals said. “It’s $700 for a beat-up building, and now I need to spend over $700 (a square foot) to get the tax credit. I can’t do that. The economics in Baltimore, in Wilmington, in Philadelphia and you know parts like Raleigh and so forth, you can buy a building, do your construction and qualify.”

In addition to the factories and tanneries of Fishtown and No. Libs, another part of Philadelphia commonly becoming apartment complexes are churches. Since 2010, 47 area churches have closed or have been scheduled to close. Michals said the Archdiocese has a whole list of properties “you can go out and buy.”

But he said churches prove trickier to turn into apartments than many other buildings. To get that important tax credit, developers usually can’t change the aspects of the original building’s height. The many arches and varying high/low ceilings of churches aren’t often ideal for residences.

When developers do pull it off, though, you get something like the Sanctuary Lofts. They’re near 23rd and Fitzwater and used to be St. Anthony of Padua Catholic Parish. The church was established in 1889. History and its doors being featured in “The Sixth Sense” weren’t enough to save it, though. It merged with another church and then closed for good in 2009. Barzilay Developments, founded by Alon Barzilay, turned it into the Sanctuary Lofts. Residents there get church-like-features such as stained-glass windows, “Cathedral” ceilings and cornices and arches that were part of the church.

The process of redeveloping historic buildings into apartments or office space can often take years, with neighbors or public officials objecting, especially to churches that were once community-gathering spots. Barzilay said opinions generally change once they realize the buildings will get blighted or torn down if they aren’t reused.

“Just because it’s historic doesn’t mean it’s protected,” he said. “And just because it’s protected doesn’t mean it’s not subject to change.”

If you want to live somewhere that used to be a factory, church or famous office building, be sure to save up, though. Rent for two-bedrooms in places like the ICON or Lofts 640 can cost over $2,500 a month. Still, Barzilay and Michals both said demand for their projects has remained high.

“What draws them to it is the unusual experience,” Barzilay said. “It’s people who want something that’s a little bit different.”