Measure the distance from the top of the attic to the floor and write it down.
Purchase 2-inch-by-2-inch lumber for rungs and 2-inch-by-4-inch lumber for the sides of the attic ladder.
Put on safety glasses, then measure and cut the 2-inch-by-4-inch lumber beams to form the sides of the attic ladder with a circular saw.
Measure where the rungs will be spaced along the side pieces of the ladder. Mark those spaces for reference points with a marker. The rungs should be spaced equally, 1 foot apart.
Drill two holes 2 inches apart and 2 inches deep into the 4-inch-wide side of each 2-inch-by-4-inch ladder side in order to create a template for the rung spaces.
Cut out the rung spaces with a jigsaw to make "U" shapes where each rung will be fastened. You now have two sides of the ladder with spaces for the rungs to be inserted.
Cut the 2-inch-by-2-inch lumber to about 2 feet in length, cutting enough beams to make rungs to fill the spaces cut on the ladder's sides.
Insert the rungs into the spaces on the ladder sides. Glue into place, then secure with a nail gun and nails. You now have a fully functional homemade attic ladder.