Among India's more ostentatious billionaires is Vijay Mallya, a liquor and airline baron with 250 vintage cars, a yacht once owned by Richard Burton and a penchant for flashy diamond ear studs.
Then there is steel magnate Lakshmi Mittal, who threw a six-day, $60-million wedding for his daughter in 2004 in a rented French chateau with performances by Bollywood stars and complimentary airfare for 1,000 guests.
Still, most Indian billionaires don't drink alcohol, grab trophy wives or act the playboy, said Subhadra Channa, an anthropologist at the University of Delhi. "It's not like in the West," she said. "These people live much more sedate lives."
Sedate isn't an obvious description for the new building, which reportedly requires 600 staff members to keep Ambani, wife Nita, their three children and Ambani's mother in the style they'll soon become accustomed to.
The rather awkward-looking structure was designed by U.S. architects using principles of Vaastu, Indian traditional geomancy akin to Chinese feng shui, to maximize "positive energy." No two floor plans are alike, and the materials used in each level vary widely, driving up the cost.
Some 1,000-plus of the Ambanis' "closest" friends are invited to the big opening party.
Despite their fabulous wealth, Ambani family members are not spendthrifts, wife Nita said in an interview published on De's blog.
She said the couple decided not to stay in the presidential suite at New York's Four Seasons Hotel recently because the rate seemed too steep, opting instead for an executive suite.
And her husband continues to buy his favorite five-pocket Dockers slacks from Macy's when he's in the Big Apple. "You don't have to spend a lot of money to be well dressed," Nita said. "You have to look and feel fresh."
But then there's the eye-popping house, named Antilia after a mythical island.
McDonald, the author, offered a theory: "Maybe it's part of a midlife crisis."
Anshul Rana in The Times' New Delhi Bureau contributed to this report.