As Sears continued to offer optimistic projections for growth, the tower's proposed floor count increased rapidly into the low hundreds, surpassing the height of New York's unfinished World Trade Center to become the world's tallest building. The height was restricted by a limit imposed by the Federal Aviation Administration (FAA) to protect air traffic. The financing of the tower was provided by Sears. It was topped with two antennas for television and radio broadcasting. Sears and the City of Chicago approved the design and the first steel was put in place in April 1971. The structure was completed in May 1973. The construction cost about US$150 million, equivalent to $ million in dollars. By comparison, Taipei 101, built in 2004, cost the equivalent of US$2.21 billion in 2018 dollars.