Plans also include construction of a 50-story, 500-room luxury hotel next door.
Building officials say the project should take five years to complete and create 3,600 jobs.
The famous skyscraper is to be renamed Willis Tower later this summer. Officials say they'd like to achieve "LEED" status, otherwise known as Leadership in Energy and Environmental Design.
It's a standard monitored by the U.S. Green Building Council.
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