Elie Tahari is planning a mega penthouse atop this Fifth Avenue co-op building.

Fresh from putting his plush Hamptons house up for sale, Elie Tahari is seeking a cash-rich partner to make his dreams for a Manhattan mega penthouse come true.

The 66-year-old Israeli fashion designer has hired real estate brokerage Town Residential to help him find an investor willing to drop $35 million on the Fifth Avenue project.

Tahari’s ambitious plans stretch back decades to when he spent $325,000 on his first penthouse at an Upper East Side condominium in 1979, later buying his second penthouse in the building in 2011 for $4.2 million.

He has also been trying to secure air rights for 12 years to build an additional two stories atop the building and he has finally gotten the green light, has started to build, but is looking for funds to complete construction.

According to Benjamin Benalloul, Loretta Shanahan-Bradbury and Victoria Terri-Cote of Town Residential, plans for the luxurious penthouse have been drawn up by Cook/Fox Architects and the finished product will be perched on the 19th through 21st floors.

The 7,500-square-foot home will come with five bedrooms (the 21st floor would house a full-floor master suite with its own living room), seven-and-a-half-bathrooms and 7,500 square feet of interior space, while there will be an additional private roof deck with views of Central Park.

Tahari’s spokesman told the Wall Street Journal, which first reported the story, that upon completion, the partners would either sell the entire penthouse, or one would acquire out the other’s 50 percent interest.

At the end of last year, the fashion magnate put his Hamptons house on the market for a touch under $45 million, almost four times the $12.1 million he and his ex-wife, Rory Tahari, paid for it in 2005.

This may sound like quite a lot of cash for a three-bedroom, 4,500-square-foot house, but the Sagaponack, N.Y., pad sits on two-and-a-half acres of oceanfront land in one of the wealthy region’s poshest enclaves and boasts panoramic ocean views.

A spokesperson for Tahari did not respond to request for comment.