Michael Stern was prepared for a gradual real estate rebound after buying a New York office tower in December 2009, with plans to convert it to condominiums following a housing plunge that sent prices down 31 percent.

Now, long before the final floor tile is laid or the first resident moves into the Walker Tower development in the Chelsea neighborhood, Stern's firm, JDS Development Group, and its partner have increased prices on units at the building 13 times.

"I didn't let the market conditions of the day dissuade me," Stern said of his 2009 deal. "But I can't say I thought prices would be quite as lofty as they've proven to be."