The first step to building this bookshelf is to cut the two shelf standards, the vertical pieces on each side of the bookshelf. Using a Table Saw or Circular Saw, cut two pieces of 3/4" plywood 12" wide x 28-1/4" high. Set these two pieces aside for the moment.
Next, you'll need to cut the three shelves. The top and bottom shelves are cut to 12" x 47", whereas the center shelf will be cut to 11-3/4" x 47".
Finally cut one piece to 12" x 48". This will be the top of the unit, and will sit above the top shelf. Set this piece aside for the time being, as you won't need it until step 5.