As @cheechako said, are you asking about basic structure or the finish material? We're using MDO plywood
(exterior ply used in sign making) for the bulkheads (painted white) with varnished mahogany and teak
was originally finished with cedar strips, which we painted white when we got the boat way back when. We've also got some stained birch ply. Tabbing is all fir, most of it ripped from 2x4s.
Our boat is fiberglass, very traditional. Most people think she's a wooden boat when they look quickly.