This page trys to describe the basics of building a simple bookcase.  The plans offered at the bottom of this page can be easily altered to any height or width. This bookcase is 41" tall by 42" wide and was made for my grandson Michael's bedroom. There is a short back to the top shelf to help keep stuff from sliding off and a toe kick under the bottom shelf, cause kids will be standing on it! I used red oak for my shelves, to match other furniture in the room, but, ash, maple, cherry, or any hard wood is fine. I wouldn't recommend pine as it is soft and the joints would tend to get loose and fail.  I won't go into detail on how to cut the shelves and sides to size. I'll start with cutting the "blind dados" that the shelves will fit into.
Make sure you follow all safety precautions that come with your tools. Keep your fingers on your hands!
First we need to set up our stack dado head cutter to 3/4", or more precisely, the thickness of your shelf stock. My stock was just a hair under 3/4" so my joint was sloppy. I needed to remove one of the standard cutters, and replace it with a narrow cutter, then shim up to the correct width with cardboard shims between the cutters. This is done by trial and error. Set up the blade, do a test cut and see if your shelf stock is snug. This is important. So you want to get it right.