Choosing a material for your homemade bookshelf is the first step. Almost any material will get the job done, so appearance can be the deciding factor. Wood is a classic, and there are many different kinds to choose from. Iron, glass and steel are all good options too. Even plastic or particleboard can be made to work, if handled honestly.
Once you decide on a material, think about what the bookshelf will look like. How will it relate to the books, and how will it fit in with the rest of the room? Depending on your preferences, there is no end of possibilities. For a bucolic look, you could take two stout logs and lay hand-cut boards of irregular dimensions between them. If elegant understatement is your taste, you could build a Z-frame out of steel and connect sheets of tempered glass to the diagonal bar. Should you desire a stately Victorian bookcase with arched molding and decorative scrollwork, you could fashion it yourself with patience and precision. Or you could go in a more modern direction and cobble together Tetris blocks of plastic draped in neon-colored curtains. Just about the only thing to avoid is the Soviet austerity of an unadorned rectangle, since that's the default bookshelf in many people's homes.
With a design in mind, your next task is to engineer the bookshelf. Your concern here is to make sure that the finished product will be stable and safe. Be sure that your design can bear the weight of hundreds of pounds of books and that the base will be wide enough so that your bookshelf won't topple over. If you aren't sure about the integrity of your design, take your blueprint to a hardware store or a friend with home improvement skills, and ask for advice.
The actual construction of your bookshelf is a treat, not a chore. Approach it in that spirit. Tighten those screws. Make the shelves absolutely level. Do it right, and have fun with it. You could make a project day out of the assembly, or you could work on it a little bit at a time on spare evenings. Invite family or friends to help, or use the occasion to get some alone time. Along the way, you'll have an opportunity to get more familiar with building and materials. It's a good, goal-oriented, hands-on project that can be very satisfying, so long as you approach it with a relaxed frame of mind.
After building the bookshelf, you may want to paint or otherwise decorate it. Consider painting a mural, hanging a small plant, or installing lamps. Here you can play with colors, textures, contrasts, lights and lines. A bookshelf can be as conspicuous or as subtle as you want it to be.