The most important thing to know when constructing a ladder is that cheaper is not better. All wooden materials used to build a ladder should be either strong oak or construction grade lumber. The materials required include two 12 foot long 2 by 4s, two 8 foot long 2 by 3s, exterior wood glue, 2 and a half inch deck screws, clamps, circular saw, hammer, chisel, drill and measuring tape.
First, clamp the two 12 foot long 2 by 4s together. Measure to eight inches from the top and bottom of each piece with measuring tape and mark this point with a pencil. The top and bottom rungs of the ladder are attached at these marks. Measure 2 1/2 inches from each mark, moving towards the center.
To find where to place the rest of the rung notches, measure from the eight inch marks at either end of the uprights. From there, make marks in 16 inch increments. This is where the center of the rung should be. Mark off 1 1/4 inches from either side of these marks for the notches.
With the circular saw set to a depth of 1 1/8 inches, cut along the end mark for each rung. Then, cut again a quarter inch away from these marks. Knock out the wood with a hammer and smooth out the notches with a chisel.
Remove the clamps that join the uprights together. Cut the eight foot long 2 by 3s into 19 inch long rungs. For the purposes of this ladder, one piece will be left over. Apply wood glue into each of the notches. Insert the rung into the notches until it is securely placed between the upright pieces. Screw each rung into place with four deck screws, two screws to each side of the rung.