Burj Khalifa is a megatall skyscraper in Dubai, United Arab Emirates. It has a roof height of 829.8 m making it the tallest building and the tallest structure in the world. Construction of the Burj Khalifa began in 2004, with the exterior completed 5 years later in 2009. The primary structure is reinforced concrete. The building was opened in 2010 as part of a new development called Downtown Dubai.