The principal advantage to building something yourself is making it to best suit your needs or lifestyle. Few woodworkers can resist the temptation to alter the plan they begin with. However, shelves and bookcases need to be built according to a few basic design guidelines to ensure that your piece will be functional as well as good-looking.
If all books were the same size and shape, bookcase and shelf planning would be simple. But that's not the case. For attractiveness as well as stability, the size and spacing of shelves depend on what you'll put on them. Books vary greatly in size, and if you want to have entertainment equipment in the same unit, you'll need shelves from 18 to 20 inches deep (for most systems) and spacing between shelves customized to fit your stereo, speakers, and accessories.
Shelving units that accommodate both books and audiovisual equipment are often built as modular components. A deeper unit holds the large equipment, and side or top units provide book or display storage.
You also must consider the shelving material's span limit—how far an unsupported shelf will span under load without sagging or breaking. Solid hardwood boards of 3/4-inch thickness, for instance, span a greater distance than particleboard of the same thickness.
Design shelves with their users in mind. As shown, men generally have a greater maximum reach than women, and teens can reach higher than children. While that may seem obvious, building shelves that no one can access is a waste of time and materials. Likewise, shelves shouldn't be too low to be used easily.