Very much depends. The foundation is always concrete, although for single-family or duplex homes the floor being concrete would pretty non-standard (that's usually wood, tile, or faux-wood e.g. vinyl, laminate). The framing is generally lumber. The exterior siding can come in any number of forms: stucco, wood, metal, vinyl, brick, etc. Brick in particular is rare on the west coast, FWIW, due to seismic conditions, but is much more common in the east.
