“The Man in the Ceiling,” based on Mr. Feiffer’s 1995 young adult novel about a boy cartoonist named Jimmy Jibbett, will have its world premiere May 30 through June 25 at the well-regarded Bay Street Theater in Sag Harbor, N.Y. The musical has taken 21 years to reach this point, coming together as a collaboration among three illustrious principals, each working in an unaccustomed role.

Image A copy of Mr. Feiffer’s book. Credit... Christopher Gregory for The New York Times

While Mr. Feiffer wrote plays earlier in his career, this is his first musical. Mr. Seller, the director, is best-known as the Tony Award-winning producer of “Hamilton” and “Rent.” (He’s venturing into TV, too, producing the high school drama teacher series “Rise” for NBC.) And Andrew Lippa, the composer and lyricist, is also acting, portraying Jimmy’s Uncle Lester.

During one tricky moment in the rehearsal, Mr. Lippa (“The Addams Family,” “Big Fish”) stepped out of character and back into his role as composer. When the actors found they didn’t have time to move from one part of the stage to another during “Getting It Right,” the opening number, he suggested adding a little vocalizing to bridge the timing gap.

He ran to a piano to tap out the four notes. “Is that a good thing?” he asked. “That’s a great thing,” answered Spencer Liff, the choreographer.

“Andrew was enriching that moment,” Mr. Seller said later of his longtime friend. “I always defer to my creators.” Now both 52, they’ve known each other since both were 6 in Oak Park, Mich., and Mr. Seller’s parents bought a house from Mr. Lippa’s parents.