a high-rise building is defined by its height differently in various jurisdictions. it may be only residential, in which case it might also be called a tower block, or it might include other functions such as hotel, offices, or shops. there is no clear difference between a tower block and a skyscraper, although a building with fifty or more stories is generally considered a skyscraper. high-rise buildings became possible with the invention of the elevator (lift) and cheaper, more abundant building materials. their structural system usually is made of reinforced concrete and steel.