Colleagues describe Joe Massaro as a can-do kind of guy.

When he heard that 11-acre Petre Island in Lake Mahopac was for sale, the 58-year-old retired contractor spent five months going back and forth to the island by motorboat looking for the owner, leaving notes and dodging dogs protecting the property. When Massaro finally found the owner, he traded him the island for a home on the lake that Massaro and his wife, Barbara, owned.

That characteristic persistence would serve him well when he discovered the island came with an added perk: Frank Lloyd Wright had made preliminary drawings in 1950 for a house on the island for a previous owner, and Massaro made it his mission to built it.

When the 5,000-square-foot single-story, four-bedroom home constructed of glass, concrete and mahogany wood is completed this fall, Wright experts believe it will be the only Wright home design built after his death in the location for which it was intended.

A.K. Charoudi, the owner of Petre Island when Wright drew the plans, had completed the project's guest cottage but ran out of money before the main house could be constructed. Dod Charoudi, A.K.'s son, provided Massaro with the drawings.

The home's most dramatic feature is a 28-foot cantilevered section jutting over the lake, so low that it practically rests on the water. This cantilever is believed to be the largest that Wright ever designed -- almost double the size of the 15-foot cantilevers that distinguish Wright's most famous home design, Fallingwater, near Mill Run, Pa., with multiple levels looming over a waterfall.

Of about 1,100 designs the prolific architect created, only about half were built during his lifetime. A number of unbuilt Wright designs, both residences and public buildings, have been constructed since the architect's death in 1959.

According to the Frank Lloyd Wright Foundation, established in 1940 as the repository of the life work of Wright, only those designs built under the auspices of the foundation's Original Unbuilt Program, completed by architects trained at the Frank Lloyd Wright School of Architecture, can be designated a Frank Lloyd Wright Design.

Massaro engaged in a brief legal battle with the foundation, and neither side is at liberty to provide details. But the upshot is that Massaro will have to call his house "inspired by Frank Lloyd Wright" rather than a Frank Lloyd Wright Design.

"We just couldn't get together," observes Massaro. "But I think they made a big mistake."

Massaro, tall and athletic with a New Yorker's rapid-fire speech, dismisses problems with a brisk "fuggedaboud it!" He feels the same way about the opinion of the foundation. Although he was not a Frank Lloyd Wright buff at the beginning, now he is determined to see the house built to Wright's specifications -- no matter what it's called.

"I took it on as a hobby," Massaro says. "I said: 'Let's see how far we can push this.' "

Massaro struggled for five years to get building permits from a variety of entities, but in the interim sold his HVAC contracting company, which provided him with the funds to build the house. He refuses to say how much it will cost, but his standard line is: "I budgeted $500,000, and I have exceeded that." Other sources close to the project estimate between $1.5 million and $3 million.

Even without the endorsement of the Wright foundation, the Massaro house is garnering attention from the architectural world. "Many of the houses that are being constructed now are being built according to plans, but not where Wright sited them," says James Libby, a filmmaker who is producing and directing a documentary on the house, expected to be completed in the fall.

"One of the most interesting aspects of Wright is his philosophical concepts, his organic architecture, buildings that are married to the ground. We are using this house to explore these ideas," Libby continues. "There is absolutely no mistake about where this house belongs."

That becomes evident as soon as you encounter the "whale rock." The entrance to the Massaro house is fashioned around a massive boulder, approximately 12 feet wide, 12 feet tall and 60 feet long, that naturally occurs on the island. The "tail rock" -- part of the same stone that emerges farther along -- will form a wall for the dining room and a bedroom.

According to the Wright foundation, there have been 15 "built unbuilt" designs constructed under the foundation's aegis since 1959, including homes and public buildings. The list includes Monona Terrace Convention Center in Madison, Wis., designed in 1938 but not constructed until the late 1990s, and Blue Sky Mausoleum in Buffalo, N.Y., designed in 1928 and completed in 2004.

A 16th structure, a private home originally designed in 1956 for Panama City, is going through the permitting process for construction near Santa Rosa in Sonoma County, under the supervision of Taliesin architect Arnold Roy.

Though one can never know what design changes might have taken place during the construction process if Wright had been alive, foundation board chairman Vernon D. Swaback believes that those projects completed by architects trained by the school, based at the Taliesin and Taliesin West campuses in Wisconsin and Arizona, respectively -- offer the best odds of accurately predicting and executing the late architect's vision.