“It has such incredible potential and has been totally underutilized,” enthused Ivanka Trump, executive vice president for development and acquisitions for the Trump Organization and Mr. Trump’s daughter, who is perhaps better known for her lines of women’s jewelry, shoes and handbags.

“You just couldn’t build something like this today,” she said, “having a nine-story glass-top atrium, having solid granite turrets, the level of detail carved into the stone. There is unbelievable wainscoting detail and incredibly intricate molding.”

Ms. Trump, who attended Georgetown University and graduated from the Wharton School at the University of Pennsylvania, has been intimately involved in planning the interior renovation of what will formally be known as Trump International Hotel, the Old Post Office Building. The project will also incorporate an adjacent annex built in the 1980s, to include a 13,000-square-foot ballroom and 36,000 square feet of meeting space.

The main building will have 271 rooms — prices to be determined — including two “presidential” suites in the former postmaster general’s office, 3,600 and 5,000 square feet in size.

The hotel rooms “will be the largest of any of the rooms in D.C.,” Mr. Trump said. “We have on average 16-foot ceilings — unheard-of in a hotel — and soaring double-bay windows. You look at these four-to-five-feet-thick granite walls. Today, you couldn’t even buy a piece of it. When the U.S. was so rich, this is the way they would build them.”

While the Trump hotel portfolio numbers nine at the moment, the addition of hotels in Vancouver, Rio de Janeiro and the Old Post Office will bring the number to 12 by 2016. The Old Post Office will include street-level restaurants, a cafe and a library. Its atrium is to have a fitness center, the 4,000-square-foot Mar-a-Lago spa by Ivanka Trump, and meeting space.