Long before he was elected president and attended the United Nations General Assembly, Donald Trump wanted the deal to rebuild the structure in New York City.

Ahead of this week's UNGA, the president reminisced to reporters aboard Air Force One how he wanted the contract to rebuild the facility in the early 2000s. In 2005, Mr. Trump complained to Senate committee that the developer responsible for the redevelopment of the building wasn't up for the task.

"I offered to rebuild it at a tiny fraction of what they were going to build it for," the real estate mogul told reporters aboard Air Force One this past week.

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Mr. Trump, asked by reporters if he'll think back to his real estate days when he returns to the U.N. compound, spoke of his real estate credentials.

"I was a very good real estate developer," the president reminisced. He added that he had correctly predicted "it will end up being much more" than expected.

"They didn't even know what New York steam was, versus a boiler," he said of the developers. "They knew nothing."

Mr. Trump estimated that he could have completed the project for about $500 million. He would have used marble instead of terrazzo, which is much more expensive, he explained.

The U.N. compound was largely built between 1949 and 1952. Over time, it no longer conformed to safety and fire codes, or to security needs. The U.S. provided about $488 million to help pay for the renovations, according to a 2015 Government Accountability Office report.

Mr. Trump is slated to meet with a variety of world leaders at the U.N., as tensions with Iran are on the rise and as he defends his phone call with Ukraine's president in which he admitted he discussed the Biden family.

The president stopped by to listen for about 10 minutes to the proceedings of a daylong summit on climate change, before leaving to attend a religious freedom event.

During last year's U.N. General Assembly, the president devoted part of his speech to defeating the "ideology of globalism."