YOU'RE GONNA HAVE TO serve somebody," trills Zack McKown as he tries to explain his nearly 30 years of collaboration with partner Calvin Tsao. It's not often that you hear an architect quoting a Bob Dylan song when describing a business philosophy, but Tsao & McKown Architects is far from the typical firm. Since the duo—Tsao, 60, and McKown, 61—opened their office in 1985, they have worked for a variety of clients, from bold-faced names like Ian Schrager (an apartment and bar at Morgans hotel in Midtown Manhattan) and André Balazs (a 47-story condominium in Lower Manhattan) to the decidedly lower-profile, like...