Willis Tower is commonly known as Sears Tower.it is the tallest building in the United States and the seventh tallest Freestanding structure in the world.(source)

Building Name- Willis Tower
Building Type- Office, observation, communication
Location- United States
Construction Started- 1970
Constraction Finished- 1973
Architectural- 442.1 m (1,450 ft)
Tip- 527 m (1,729 ft)
Top floor- 412.7 m (1,354 ft)
No of Floors- 108
Mo of Lifts- 104 (With 16 double-decker elevators)
Architect- Skidmore, Owings and Merrill