Rustic Bookshelf with 2x2 Face Frames

Drill 3/4" pocket holes along the side edges of the sides (add holes along the top edge too, for attaching the top later). Attach the side trim to the outsides.

If you don't have a pocket hole jig, carefully predrill and use 2-3/4" trim screws to attach the legs in the next step instead.

Attach the 2x2 legs to the sides.

Attach the top support pieces.

Build the bottom shelf first, the same way as the other shelves in the next step, then attach it to the bottom of the case.

Build the remaining shelves and insert into the bookcase. Fixed shelves are recommended over adjustable ones here, since they give you something solid to attach the back planking to.

Build the top with 3/4" pocket holes and attach to the case. If you don't have a pocket hole jig, cut three 2x2s 11-1/4" long and screw between the top supports, then use these as an attachment point for the top boards instead.

Add the back planking, nailing to each fixed shelf. Tongue-and-groove boards or plain 1x4s both work as lower-cost substitutes.

Sand every surface and finish.