Disclaimer: I am not a lawyer, and this personal opinion is not legal advice.
Architecture/buildings are indeed often protected by copyright, however copyright laws for making images of these differ by country.
In the UK we have a Freedom of Panorama exception to copyright which means that images of buildings/architecture/public art are exempt from infringing the copyright of the buildings themselves, for any purpose: either commercial or non-commercial, as long as they can be seen, drawn/photographed from a public place.
As far as I am aware, I believe the US has something similar, but sadly they don't extend the same freedom to commercial use (such as advertising). From what I've been able to ascertain, some images of buildings are trademarked, for example the Empire State Building. So you'd probably need to obtain permission/a release to use such an image for commercial purposes. Perhaps you should really ask a lawyer.
The Empire State Building has a website to apply for permission to use the name, and the image. http://www.esbnyc.com/business-esb/licensing