Willis Tower
Sears needed  of office space for its planned tower. They hired architects Skidmore, Owings & Merrill (SOM). Sears paid for construction of the building. Architects Bruce Graham and Fazlur Khan designed the building. They designed it as a nine square "tubes". It was connected in a 3×3 metal wrap forming a square base with  sides. All nine tubes would rise up to the 50th floor of the building, where the northwest and southeast tubes end. The northeast and southwest tubes reach the 66th floor with the north, east, and south tubes end at the 90th. The last west and center tubes reach 108 floors. The Sears Tower was the first building to use this design. It was both cheaper and stronger. At 1,450 feet, it had more space and was higher than the Empire State Building. It cost much less per unit area. The system became successful in skyscraper construction and has been used in most supertall buildings.