Loft ladders, used daily, shouldn't be flimsy, clumsy or awkward. Their rungs need to attach at a precise angle, parallel with the floor and with the ladders' feet. Getting the angle right makes the ladder sturdy, comfortable and safe. Use typical dimensional lumber or take it up a notch and build with redwood, which is less likely to have warps and defects than pine or fir.
Measure the distance from the floor to the loft and add 12 inches. Cut two two-by-fours to this measurement with a miter saw.
Swing the blade of a radial-arm saw to the right side and lock it down at 15 degrees. Trim one end of both two-by-fours. Don't lose any of the length. The two angled ends are the bottom feet of the ladder.
Install a 1½-inch dado blade on the saw. Raise the blade on the saw 1 inch above the surface of the table.
Measure from the sharp point at the bottom end of both pieces and make a mark at 12 inches. This will be the first rung. Make another mark 12 inches from the top of each piece, for the top rung. Measure the distance between the notches. Make marks every 12 inches to represent each rung. The thickness of each rung is 1½ inches; when rungs are centered in each notch, the distance between each rung will be 10½ inches. For example: a 8-foot ladder should have 7 rungs spaced 10½ inches apart.
Place one of the marked two-by-fours on the bed of the saw, with the sharp point facing the fence. Turn on the saw and cut notches centered at each mark.
Swing the saw blade to the left side and lock it down at 15 degrees. Place the other two-by-four on the saw. Cut a notch at each mark with the sharp point facing the fence.
Cut 18-inch lengths from the remaining two-by-fours, one for each rung on the ladder.
Build the ladder on its side. Place the notched pieces face up across two sawhorses. Apply wood glue to the notches. Fit the ends of the 18-inch two-by-fours into one of the notched two-by-fours to form half the ladder. Place the other notched two-by-four on top of the rungs, fitting the ends of the rungs into the corresponding notches on the upper two-by-four.
Place clamps across the assembly, alternating them from side to side. Lay the assembly flat across the sawhorses. Drill two holes, evenly spaced through both pieces for each rung. Use a drill/driver with a 3/16-inch bit.
Insert 3-inch screws in the holes. Drive them in with the drill/driver. Allow the glue to dry overnight and remove the clamps.