CHICAGO (AP) — Willis Tower in Chicago is preparing for a $500 million face-lift under an ambitious plan Mayor Rahm Emanuel supports.

The renovations call for six levels of entertainment, restaurant and retail space, which could become an attraction for thousands of building employees and 1.7 million yearly visitors drawn to the observation deck on the 103rd floor.

A revamped plaza will include a 30,000-square-foot outdoor deck and garden as well as a three-story transparent glass structure set atop the existing plaza.

The skyscraper, which is now the second-tallest building in the nation, was opened as Sears Tower in 1974. The building is owned by private equity and real estate investment firm Blackstone Group and its Chicago affiliate Equity Office Properties.

A Blackstone official says construction is expected to begin in the first quarter of this year with completion scheduled for 2019.