To build your own bookcase, first use graph paper to create a to-scale blueprint of the shelves you desire. Space out the shelves with at least 18 inches between them. Use a level and do a rough sketch with a pencil on the wall of the inset. Design the shelves in halves or thirds to make room for the supports. Use 1-by-10-inch boards and begin to cut the boards to fit the space.
Place the bottom section of vertical boards on the ground and place L-brackets on either side of the boards. Mark the spot on the wall where the brackets belong, and then create screw holes with plastic anchors where the markings are. Secure the brackets into the anchors place the boards against the L-brackets. Screw the brackets into the boards on each side.
Begin placing the lowest horizontal shelf onto the tops of the vertical boards. Repeat the L-bracket steps to secure the horizontal boards in place, creating the first shelf space. Using the design you created on the blueprint, build the bookcase from the ground up, one section at a time. Paint or stain the boards to suit the room's decor. If desired, create 1/2-inch trim for the front edge of the bookcase to create a more formal look.