When the principal of Public School 43 in Far Rockaway, Queens, told a developer two years ago that he needed another building for the students that new housing was bringing to the area, he got a surprise answer: "O.K., I'll build it."

"I'll never forget that conversation," said the principal, John M. Quattrocchi.

A ribbon-cutting ceremony is to be held tomorrow for the $2.5 million annex built by the developer, Ron Hershco, at his company's expense. It opened on Sept. 8, the first day of school, and houses nearly 200 students. In the past, such students had to sit in a room where two classes were taught at once, or in one of the five red trailers parked across from the main building.

More than 1,400 students are enrolled in P.S. 43, which opened in 1996 and was built to hold 1,200 pre-kindergarten to eighth grade students, Mr. Quattrocchi said.

School overcrowding has been a problem in New York City for years, and rapid development on the Rockaways peninsula in Queens has aggravated the situation there. New housing has been springing up across the Rockaways in the past decade, filling schools beyond their capacity, said Councilman James Sanders Jr. of Queens.

While the city sometimes demands that housing developers help pay for school construction, Mr. Hershco's offer to build an annex and pay for it himself was a first in recent memory, said a spokesman for the Department of Education, Margie Feinberg.

Such a donation offers two clear-cut benefits: it provides the community with a much-needed school building and the developer with favorable publicity, said Jonathan Gaska, the district manager for Community Board 14.

In the last three years, United Homes has built 500 apartments in the Rockaways, bringing in more than 300 families to the five-block radius around P.S. 43, said its project manager, Or Zohar. One building is across the street from P.S. 43, on Beach 29th Street.

Mr. Hershco, 39, who moved to Queens from Israel in 1992, began building homes there eight years later, when he noticed that the neighborhood was booming. But, he said, "I couldn't figure out how the schools were going to support the families." Mr. Hershco had planned to build near P.S. 43, and was surprised to learn that students there were attending classes in trailers.

"I figured that if I'm not going to do something, this whole place will be overwhelmed, because I'm bringing in 300 families," he said. "I make my living in the area, so at least I could do something for the community. There was no other way for me to give back."

Soon after meeting with the principal of P.S. 43 in early 2003, Mr. Hershco approached the city with his proposal. Ms. Feinberg said the city made no special accommodations for the developer, who built on a strip of land he had purchased a block away from the main building, across from the classroom trailers.

Navigating city government was fairly easy, Mr. Hershco said, but building a school for the first time was challenging. The 10,700-square-foot building had unique considerations, he said. For instance, waters from the nearby Atlantic Ocean flooded P.S. 43 during its construction, so the foundation of the annex rises about five feet above ground, he said.

The new building will not eliminate overcrowding at P.S. 43, but it helps, said Mr. Hershco, who does not plan to build any other school facilities because it is "very exhausting."

Councilman Sanders, who said he planned to attend the ribbon-cutting ceremony, said the new building set an example for other developers.

"It's not that we solved the problem, it's that we've created a new model," he said. "If every developer who came in did the same, we would have solved the problem of overcrowding."