What you'll need
1 piece of 2"x 10" x 12' lumber (cut in half)
2 pieces of 1"x 10" x 8' lumber cut into 32" sections
"L" brackets (4 per shelf).
A saw or router.
Piece of thin hardboard or 1/4" plywood.
Brads (1/2") and screws (#8 3/4" long)
Sandpaper, stain, and paint.
Drill and drill bits
Screwdriver and hammer
Cut (or have your lumberyard cut) a 2"x10"x 12' piece of lumber into two pieces 72" long. These two pieces will form the sides of your bookcase.
Cut (or have your lumberyard cut) 2 pieces of 1"x10"x8' lumber into three sections each. These 32" sections will form the top, bottom and shelves of the bookcase.
Sand the edges of all the boards. Paint or stain all the boards as well as the piece of hardboard or plywood.
Determine the optimum spacing of your bookcase shelves (depends on the size of your books) and mark the spacing on the sides of the bookcase.
Attach "L" brackets to the sides of the bookcase aligning them so the shelf heights will match your requirements. (Put the brackets 3" from the front and 3" from the rear of the bookcase sides).
Fasten the top shelf to the L brackets on both sides of the bookcase and then work your way down, attaching the shelves as per your layout. You may want to position the top shelf 1" from the top of the bookcase for appearance.
Paint the "L" brackets so they blend in with the bookcase color.
Cut the hardboard to fit the back of the bookcase and attach it with the brads.