It's sort of like doing kitchen cabinets. The bench will consist of two base cabinets, 18" wide x 24" deep x 34½" high, one a four drawer unit, the other one drawer plus two sliding shelves behind a door. They'll support a 1½" thick bench top between them. I haven't figured out what the top will be made of yet.
Each cabinet has three major construction steps: the case, face frame/trim, and drawers/shelves. Last weekend I cut out all the pieces for both cases from ¾" veneered plywood, as well as cutting a few dadoes and rabbets in . A single 4' x 8' sheet turned out to be enough for both with a little left over. I also needed to get some 2' x 4' sheets of ¼' MDF (medium density fiberboard) for the rear panels and case floors. I also cut the necessary dadoes and rabbets for the top and bottom frames.
The cases are pretty simple. I used the same technique as for the bookcases I built a few years back. Basically it's two side panels made from ¾" plywood glued and screwed to rectangular header and footer frames, also made of plywood. A piece of MDF goes on the back, and the face frame will eventually go on the front.
Yesterday I glued up the header and footer frames. Today I cut some rabbets and dadoes in the side panels to fit various pieces of MDF (the back panel and the floor, which sits on top of the footer frame). There were also some other glue-ups, including adding a couple of cleats to the header frame for attaching whatever I come up with for a bench top.
(I made a stupid error here. I was very careful to ensure that the mounting holes on the cleats were exactly the same distance apart on every cleat, and then I made a template of exactly the same size and spacing out of MDF so I could easily transfer the measurement to the benchtop when I make that. Except I mixed up my width and my depth. I was thinking the cleats ran front to back on the cases, when they actually run side to side. The template would be much more useful front to back. It's not fatal. It just makes it trickier to get everything aligned in the end.)
The last thing I did today was assemble one of the cases, which is now all clamped up as the glue sets.