"Avengers Tower, formerly known as Stark Tower, is a high-rise building complex located in Manhattan, New York City, owned and constructed by Tony Stark. The tower is powered by an Arc Reactor that makes it capable of running itself for over a year. The top ten floors are all devoted to research and development." - MCU wikia
For comparison, this is how it looked at the end of
The Avengers (after sustaining some considerable damage during the Battle of New York):
Avengers Tower, which will likely function as The Avengers' primary headquarters from now on, will next be seen on-screen in the 2015 Marvel blockbuster
Avengers: Age of Ultron.