Downtown real estate mogul Dan Gilbert is closing in on a deal to buy the Buhl Building and its 652-space parking deck downtown, two sources familiar with the negotiations told Crain's Friday.

The 27-story skyscraper at 535 Griswold St. would become the most recent high-rise the Quicken Loans Inc. and Rock Ventures LLC founder and chairman has added to his real estate portfolio.

Other high-profile purchases include Ally Detroit Center (formerly One Detroit Center), the Book Tower, the David Stott Building and the former Compuware Corp. headquarters, now known as One Campus Martius.

One source said the deal is a few months away from closing and Gilbert had the properties under contract. The other source said a deal was close. Both asked for anonymity because they aren't permitted to publicly discuss the negotiations.

Whitney Eichinger, vice president of communications for Rock Ventures, said the company "cannot comment on rumor and speculation."

The expected sale price is not known.

The Buhl Building, which owner Chicago-based Heico Cos. has been marketing for sale through the Chicago office of Cushman & Wakefield, has been up for sale since January 2016. A Canadian investor, Ronald Lanthier, had the building and its parking deck under contract with a $75.5 million plan last year but the plan collapsed.

The building is 385,000 square feet and opened in 1925, according to Historic Detroit, which tracks Detroit buildings and architecture history.

Gilbert, who moved Quicken Loans downtown in 2010, has become the city's most prominent real estate investor and developer since then.

He owns more than 95 properties totaling more than 15 million square feet in and around downtown, according to figures from his Bedrock LLC real estate development, ownership, management and leasing company.