It's surprising how much money something as simple as a bookcase can cost. After all, it's just a bunch of boards attached to other boards. Worse, many commercially sold bookcases are made out of weak and ugly particleboard. Fortunately, you can build your own bookcase over the course of an afternoon in a project suitable even for novice woodworkers.
Drill two parallel lines of six holes each through the faces of both 72-inch planks. Each line should be 3/8 inch from one of the long edges of the plank. Space the lines 3/8 inch, 12 inches, 24 inches, 36 inches, 48 inches, 60 inches and 71 5/8 inches from one end. The last hole is 3/8 inch from the opposite end. Use a drill bit 1/8 inch narrower than the diameter of your wood screws.
Drill two holes in each end of every 36-inch board. Drill them on each centre, one hole 3/8 inches from either end. Use the same drill bit you did in Step 2.
Sand all surfaces of your lumber, using rough-grit sandpaper.
Set both 72-inch planks and two 36-inch planks in a rectangular frame. Screw them together by driving wood screws through the pilot holes you drilled in Steps 1 and 2.
Set the remaining 36-inch planks inside the rectangular frame, running parallel to the 36-inch planks already installed.
Install each plank into a different set of pilot holes, just as you attached the planks in the rectangular frame.
Set the wooden sheet on the back of the rectangular frame, its edges aligned with those of the frame. Attach it using finishing nails and your hammer. Put one nail in each corner. Space nails every six inches along each edge.