Shelving Unit Design
Define what the shelves are for. They could serve as a place to keep your books with their spines (and titles) in plain sight, or to display art objects, collectibles, photographs or even knickknacks to decorate the room. The purpose of the shelves will help determine the depth they need to be. According to woodbin.com, the proper depth (from front to back) for a general-purpose shelving unit is 10 to 12 inches, although specialty shelving units may vary in depth.
Measure the space to determine the height and width of the shelving unit (or units) you will build. Keep in mind that bookshelves and storage shelves will sag in the middle under the weight of their contents and a smaller span will reduce the amount of sag. With this is mind, it's advisable to erect two narrow units to fill the same space that one wide one would occupy. A good rule of thumb is to keep shelves 30 to 36 inches wide to limit noticeable sag.
Determine how you would like to start the shelf at the floor and to finish it at the ceiling. You can fashion baseboard and crown molding across the front to match the current decor of the room and give it a truly built-in look, or build it more to resemble portable furniture with a toe kick at the base and a smaller profile molding at the top.
Decide on the material from which you'd like to construct the shelves and the kind of finish to apply, or opt for using a prefinished material. Paint-grade and stain-grade material can be costly and the price may vary by wood species (assuming wood is the material you use), so take this into account when designing your shelves.
Building the Shelving Unit
Measure and size your material, then cut it to the proper width with a table saw or skill saw, or use pre-cut shelving material available at most home-improvement stores. Once you have cut the top and bottom piece of each unit, you'll want the shelves in between to be cut slightly smaller than the inside dimension.
On the bookshelf or storage shelving sides, drill holes for the shelf-mounting pins with a store-bought or homemade template, or use dado slots for shelf clip tracks, available at most home-improvement stores.
Using an air nailer and screws, attach the top and bottom pieces to the sides, creating a box shape.
Size ¼ inch backer material (like plywood or melamine) to match the exterior dimensions of the shelving unit and attach it to the back using glue and staples or nails.
Repeat as necessary to make the required number of shelving units.
Place the nearly completed unit in the space where it belongs and attach it to the wall. Using properly sized finish-grade material, build a face frame in place on the shelving unit to give it a refined look. The face frame should be flush to the wall, floor and ceiling to close any gaps around the case itself, but may overhang the interior of the shelving unit slightly. Apply face frame material to the fronts of the shelves, trimming their depths to match the interior depth of the shelving unit if necessary. Insert shelf pins or clips into the proper slots or holes, insert the shelves and enjoy.