I recently built my own bookcase. Not from a kit, not from a box; from real lumber, screws, and elbow grease. Took only 3 1/2 hours to complete.

The full photo gallery can be found here.
I've broken this article up into several sections, listed below:
Materials bill came in right around $100. I used pine, a soft wood, for the shelves and sides. Shelves are 4' long and 1' wide. Sides are 12' long and 1' wide, or so it said at the store (more about that later). Both shelves and sides were 5/8" thick. There are 6 shelves plus the top of the bookcase. Each shelf was $6.79 and each side was around $12. I also bought a 4' long, 3" wide piece of red oak for the front of the bottom shelf. That added another $5 or so. Had to get red oak because they didn't have that size in pine. Got the wood and everything else at Home Depot. Worth noting: I bought all the wood in precut sizes. Didn't have to saw anything for this project.
Also bought a pack of 48 shelf supports, the kind that come with any other bookcase. The shelf supports are 3/16". I picked up two small packages of metal screws. The screws are 2" long with an 8 diameter. The diameter thing is kind of weird; on the side of the package there's a little table. You find the "8" and it tells you the size of the screw.
This, essentially, is all that goes into a bookcase.
I used a variety of tools for this project, some of which I didn't own at the start and which add to the overall materials bill.
The most important part of this project is the measuring.
Drilling the holes for the shelf supports was easily the most tedious task of the project.
After drilling all the holes for the shelf supports, it was time to frame up the bookcase. The frame here consists of the two sides, a shelf piece for the top, a shelf for the bottom, and the red oak face piece.
This bookcase is too tall and pine too soft to have the frame standing alone with all of the shelves put in randomly.
This is the finished bookcase in all its glory:
In this picture, you can see all of the shelves and even the red oak bit at the bottom.
Lessons learned:
- Always measure the lumber by hand at the store. Apparently lumber's an error-prone commodity and is often cut to a slightly wrong measurement. In my case the error was acceptable, but I almost had to buy two new sides.