system
Given the following post, respond as if you're commenting on Reddit:
human
[Avengers: Age of Ultron] Did Tony Stark actually buy that building?

The one he collapses onto the Hulk.  Buying a building seems like something that would involve lawyers and lots of paperwork, and not something that could be done in only 3 seconds.  Hell that's not even enough time for whoever owns the building to respond to an offer.
gpt
Unless it was up for sale with a buyout price, no, he likely wouldn't have been able to literally buy it then and there. But what he could do was put an offer on it. A pretty high one, probably a lot more than the building (which was still under construction) would ultimately be worth. Then when the owner(s) get wind that the building has been destroyed, taking all of the investment with it, they'll likely be all too eager to entertain that offer since it will cover their costs and net them a tidy profit as well.