Ahh... Title 17, section 120 of US Code specifically exempts me from worry here (almost). If the building is (as per assumptions of this scenario) visible from a public street, the copyright in the architectural work does not include the right to prevent the making of pictures, etc. of the work. But, unfortunately, the photographer need not just learn the 10 chapters of copyright law, there is also trademark law lingering about to dampen one's artistic zeal. This reprinted, via Educom's Edupage (16 June 1996), from the NY Times:

WHO OWNS THE "IMAGE" OF A BUILDING? In a precedent-setting intellectual property dispute, the Rock & Roll Hall of Fame & Museum in Cleveland, Ohio, is suing a photographer for infringing its trademark by selling posters made from his photo of the architecturally distinct museum. Photographers, artists, filmmakers, and publishers are concerned about the implications of allowing trademarks for buildings, but lawyers for the museum argue: "If we lose our rights on posters, we'll lose it on T-shirts and hats."

Trademark protection generally is intended to prevent someone from copying a building's distinctive shape (such as that of the famous McDonald's golden arches). The issue is whether the photographer's profits from the poster are due mainly to his own creativity as a photographer or rather to the beauty and fame of a building designed by others. (New York Times 16 Jun 96 p1)

So there! What copyright law does not take away, trademark law may.