Where’s the best place to find underground indie films in Gotham this summer? Look up.

Rooftop Films has lined up about three months worth of programming for its 15th annual Summer Series of outdoor screenings — most of which take place on New York rooftops. The summer lineup kicks off May 13 with a collection of short films unspooling at the Open Road Rooftop on the Lower East Side.

Rooftop fulfills its mission of bringing indies to auds by relying in large part on the attraction of its open-air venues. “From the beginning we got good crowds for films no one has heard of, mostly because of the novelty,” says program director Dan Nuxoll.

The homey, social-event atmosphere, complete with pre-show live music and post-screening parties to which everyone is invited, is punctuated by bigger events that help attract attention to the esoteric film selections.

Take the upcoming screening of Robert Greene’s wrestling doc “Fake It So Real,” which will include a live wrestling match from the North Carolina semi-pros depicted in the film.

“What Rooftop does is create an event out of it, and sort of smuggles these little-known films in to the audiences,” says Eric Kohn, a Rooftop programmer.

Throughout the summer screenings are held in a number of venues in multiple boroughs. A big chunk of them take place on the roofs of school buildings, in part because it’s a low-cost option, and in part because of a quirk of Gotham architecture.

“In the early 20th century, a lot of schools were built in New York with rooftop gymnasiums,” says Nuxoll. They’re rarely used these days, but they work perfectly for Rooftop’s purposes: “They’re these big, beautiful spaces with lots of legal means of egress,” he says.

(More info: Rooftopfilms.org)