How to Build a Bookshelf
When you build a bookshelf, try to make the shelves 12 or 16 inches deep so they fit most books better. Then, use a table saw to cut the boards with the good side facing up so they look better. Once all of the boards are cut, use wood glue and 2” screws to attach the sides to the base. Next, cut slots on the outside edges of the top board to it sits lower and more securely on the sides. Secure it, and the shelves if you want, with the same glue and screws that you used for the base.
Design and measure. You can build a bookshelf to fit a particular space in your home or make one that's a standard size so that it can work in a variety of locations. Measure the space where the bookshelf will sit. Decide how tall you want the finished shelf unit to be and how wide. Bookshelves are traditionally 12" or 16" deep; of course, you can customize to suit your needs. Decide if your bookshelf will have an open or a closed back. If you keep the back open, your books may lean on or touch the wall behind the bookshelf. Decide it you'll use it to house paperback, hardback or coffee table-sized books. For maximum versatility, this project uses adjustable shelving so any size book will fit. Standard bookshelves come in two-, three-, four- and five-shelf varieties, but you can make as many shelves as you want for your project. Choose your wood. The wood you use will greatly impact the finished look of your piece as well as its cost and durability. Since solid wood could cost thousands of dollars, you'll likely want to use plywood with a hardwood veneer. Choose a 3/4" plywood for the body and shelves of the bookshelf, and a 1/4" piece of plywood for the back. A plywood sheet is 4' wide, but keep in mind that a saw blade takes off 1/8". Calculate how many 8' long boards you can get from one sheet and use that to figure out how many sheets you will need. For this project, you'll need just one sheet. Choose the right saw. Use a table saw or a circular saw to cut your boards. Cutting plywood can be difficult and dangerous, so it's important to set yourself up for success. Cut your sides. Start by cutting your long boards to the width you want. Remember that standard widths are 12" or 16"; for this project, our depth will be 12". Push the wood through the saw at a consistent rate to ensure a cleaner cut.  Enlist the help of a friend. One of the challenges of working with plywood is that it comes in large 4' x 8' sheets,so it can be a bit difficult to handle on your own. Use saw horses or a roller table to also provide support. Rip a piece of ¾" birch plywood into a 12½" wide strip. If you're using a circular saw, be sure to use a straight-edge guide. Cut the strip into two 41¾" pieces to make the two bookcase sides. You can adjust this measurement up or down if you want your bookshelf to be taller or shorter. Cut your bookshelf bottom and shelves. Remember that the width of the saw blade is 1/8" and factor that into your measurements. Rip a strip of 3/4" plywood 11⅞" wide to make the shelves. Rip a second strip 12 1/8" to make the top and bottom shelves. Cut the other two strips into 30½-" pieces to make the top, bottom and two shelves. Cut the rabbet joints. A rabbet is a groove cut into a piece of wood. In this case, creating rabbet joints will allow the top of the bookcase to sit squarely and securely on the two sides. Set a saw to make a 3/8" cut. Cut a track into the end of the shelf by making cuts straight across the shelf in 1/8" increments until the track is as wide as the thickness of the plywood sides. Alternately, use a router fitted with a ball-bearing-piloted rabbeting bit to make your cuts. Drill the holes for adjustable shelving along the bookshelf sides. Since book sizes differ and your needs may change, it's best to make your shelves adjustable so that you can arrange and rearrange them as best suits you. Clamp a pegboard (this will be your template for the holes)in place so that the first holes will be 4" above and 4" below the center shelf. If you don't have a pegboard, you make a hole-drilling template out of ¾-inch pine cut to the same length as the bookcase sides. Use a drill/driver fitted with a ⅝-inch spade bit to bore a series of equally spaced holes in the template board. Use a drill bit that's the same diameter as the shelf-support pegs and drill holes 2" from the edge in 2" increments. Drill approximately 1/8" deeper than the length of the pegs. Put a piece of tape or a drill stop on the bit to guide you in drilling to the correct depth and take into account the thickness of the pegboard. Attach the top to the sides. Apply glue the length of the rabbet groove and put the top in place. Add pocket screws to secure the top. Add support blocks. If you'd like, you can use support blocks for the center and bottom shelves; they'll strength the frame without adding excessive bulk. If you do add these blocks, be aware that your center shelf will be fixed; you won't be able to adjust it. Glue 1" x 2" support blocks in place for the center and bottom shelf and secure them with finish nails Drive the nails until each head is just above the surface of the wood, then use a nail set to drive it just below the surface. Drill and countersink pilot holes for the top of the bookshelf. Attach it with glue and 2" wood screws. Put the center and bottom shelves in place. Once the top of the bookshelf is secure, attach the bottom shelf. Apply wood glue to the support blocks for the bottom shelf and set the shelf in position. Drill and countersink pilot holes in the side of the bookshelf and attach the shelf with 2" wood screws. If you decided to use support blocks for the center shelf as well, install it now as you did the bottom shelf. Attach the back panel. A back panel gives a bookshelf a finished look and protects the paint on the wall behind the bookshelf. Make sure the bookshelf is square. Tighten any screws if necessary to get the shelf to stand in place with perfect right angles. Measure and cut the back panel. Start in one corner and use 1" brads to fasten the back panel in place. Attach the trim. Trim or molding will give your bookshelf a custom look. If you've measured it to fit a particular nook in your home, the addition of trim can create the look of a built-in unit. Attach 1" x 2" trim pieces to the side and bottom edges of the bookshelf with sixpenny nails and glue. You may want to miter the corners of the trim pieces; the finished look is up to you. Once the trim is in place, use a router with a 1/2" round over bit to smooth sharp edges. Glue and nail edge molding to the shelves taking care not to split the molding. If you'd prefer to a sleeker look, use veneer banding instead of molding to cover the plywood edges. Using an iron set to a low heat, apply iron-on birch veneer edge banding to the front edges of the plywood sides, shelves, top and bottom. Then press the veneer tightly to the plywood using a J-roller. Cut the veneer to length with a utility knife. Use a veneer trimmer to slice off the overhanging edges of the veneer and hand-sand the edges with 120-grit sandpaper so that it's flush with the plywood. Sand the bookshelf. Proper sanding is essential to the final appearance of any finished surface and affects the success of the staining process. Stain will appear dark and blotchy if the surface isn't well-sanded. For best results, use a 150 grit sandpaper to remove all handling marks and raised grain. Use a hand block and/or pad sander to cover 100% of the surface with even pressure.  Sand the entire surface, don't rely on your eye to sand only the spots that look irregular to you, sand the whole bookshelf. Paint or seal the unit. The final touch is to put a protective coating on your new book shelf--whether that's paint or a clear finish. Apply primer and paint. Primer helps the wood absorb the paint more evenly for a more uniform finish. Apply a coat of primer and let it dry. Sand the unit lightly and remove the dust with cheesecloth or a soft, cotton rag, Apply a coat of paint. After the first coat dries, sand again, dust and apply the final coat. Choose a white primer if your paint color is light; choose gray if your paint color is dark. You can also have your primer tinted to match the color of your paint. Apply a clear finish. If you've chosen a more exotic wood for your bookshelf, you'll want to use a clear, polyurethane finish to highlight the natural beauty of the grain. Apply the first coat and let it dry before sanding with a fine grit sandpaper. Remove the dust with cheesecloth or a soft, cotton rag and apply a second coat. Again, let it dry before sanding with a fine grit sandpaper. Apply a third and final coat of the finish. Don't spend a lot of time applying the finish by going over and over again. Just put on a nice thin even coat. Most small bubbles will come out on their own, or you will fix them when you sand. 
Design and measure. Choose your wood. Choose the right saw. Cut your sides. Cut your bookshelf bottom and shelves. Cut the rabbet joints. Drill the holes for adjustable shelving along the bookshelf sides. Attach the top to the sides. Add support blocks. Put the center and bottom shelves in place. Attach the back panel. Attach the trim. Sand the bookshelf. Paint or seal the unit. 