By the time he passed away in Monaco last March, the British skyscraper developer Howard Ronson had paid $22.95 million, in three separate deals over three years, to amass a 32-room spread in the hugely ornate Berwind Mansion co-op at 828 Fifth Avenue. (Never mind that he reportedly enjoyed his later years on his yacht.)

Eleven months later, he’s posthumously added a few more rooms.

His limited liability corporation just paid $11 million, according to public deeds, for the building’s glass penthouse, which takes his family’s tally in the mansion to nearly $34 million. That number is likely to go up, considering that records show there are at least two other owners in the building to buy out, including the retired dress designer Adolfo, Nancy Reagan’s old favorite.

It’s not clear if his widow controls his real estate deals now, but two brokers said that the idea to buy the whole mansion piecemeal came from Mr. Ronson himself. Last year, two of the apartments were transferred to a children’s trust, with an address in the Channel Islands off France.

If that trust or the LLC buys up the rest of the mansion, the Ronson family will be the first to have the house to themselves since the Berwinds. The place was built 111 years ago by the mining magnate Edward Berwind, whose coal powered the U.S. Navy through World War I. He sold to his sister Julia, who sold to the Institute of Aeronautical Sciences—it was split into apartments in the 1970’s.

Even before this $11 million deal, Mr. Ronson’s units in the building included a ground-floor duplex with a 4,000-bottle brick wine cellar, a glass conservatory and a garden. Better yet, Madonna once spent 15 minutes lying face-up in the parlor floor’s oceanic gold ballroom, ogling its 18-foot ceilings. That unit’s mirrors hide routes to mezzanine bedrooms—which must have appealed to Mr. Ronson, whose New York business office was camouflaged by an oak-paneled waiting room.

The mansion overflows with flowery Napoleon-level luxury, from the painted ceilings and gold trim to the fluted columns, sculpted mantels and perfect moldings. But on the downside, the glass-paneled penthouse was rejected by Rudolph Giuliani in 2002, after three visits, reportedly because it didn’t have a separate formal dining room.

According to city records, the penthouse seller is T. Richard Butera, a developer and philanthropist, who married the sister of infamous bounty hunter Domino Harvey.