-wood for shelves (I used 1/4" thick red oak planks, backed with 1/4 - 1/2" thick red oak for support)
-wood for cross bars (I used 1/2"x1.5" red oak)
-shelf brackets (< 1.5", to support cross bars, need 8)
-shelf braces (look for 'mending plates' - straight brackets to support cross bars, need 8)
-wood finish (I used 50/50 tung oil/mineral spirits)
-1/2" - 5/8" wood screws
Not having a table saw or planer, I used craft wood that has already been (mostly) squared and nicely planed. I chose oak. This project could be built for much less $$ if you have the ability to cut and plane your own boards!
Step 1: Prepare the Ladder
Step 2: Add the Braces
The straight braces are screwed to the underside of the ladder steps. You might notice that when the ladder is oriented so that the back rails are perpendicular to the floor, the steps are slightly slanted. In order for the wooden shelves to be level, the metal braces need to be bent until they are level.
The square brackets are screwed to the inside of the back rails. The cross braces will be screwed into both sets of brackets.
Step 3: Cut and Install the Cross-bars
To cut with a jig saw, measure the distance from the side of the saw to the blade and set up a 'rail' to guide the cut that is this distance away from your desired cut. For instance, my jig saw has 1.5" between the blade and the side of the saw. To cut 3", I clamp a piece of wood at 4.5". This is where the T-square comes in handy. If your rail is slanted, your cut will be too!
Screw cross bars into braces. Use pilot holes before drilling - it turns out that 1/2" thick boards have a tendency to split...
Step 4: Cut and Reinforce the Shelves
The steps of the ladder are ~.75" thick. When the 1/4" thick shelves sit on top of the 1/2" cross bars, the shelves sit flush with the wooden steps.
I cut and glued supports (1/4" x 2" oak) to the underside of the shelves. The supports keep the shelves from sliding off the cross bars and prevent bending from the weight of the books.
Step 5: Assemble and Finish
The final product is meant to be disassembled - the shelves are not glued in, and the cross bars can be unscrewed, allowing the ladder to fold.