Cut the stringers
First of all, cut three stair stringers of your staircase, from 2-inch x 12-inch (2" x 12") lumber to facilitate a 3-1/2 inches stair height. Now, cut a notch in the bottom of the three stair stringers in order to fit over the piece of 2" x 4" lumber. However, make sure to cut the notch of the staircase in the same place on each of the three stair stringers.
Cut the threads and risers
Now, cut 10-inch threads from 2" x 10" lumber for each stair. Also, cut 7-inch risers from the OSB (oriented strand board). In addition to threads and risers, cut one piece of treated 2" x 4" lumber to 3-inch long.
Install the Treated 2x4s
Place of the stringer of your case stair against the wall and ask your helper to hold it tightly. Now, fit the treated 2" x 4" into the notch of the stair and press it flush to the wall of your house.
Drill through the 2" x 4"
Drill through the 2" x 4" and into the concrete floor with the help of a masonry bit. Now, gradually attach the 2" x 4" to the floor with the help of a good quality concrete nails.
Attach the stringers
Attach the first stringer of your stair to the 2" x 4". Now attach the stringer to the top stair supported with a fine quality and strong metal brackets. Grab the second stringer in the same way at the other end of the stair 2" x 4". Now, fix the third stringer halfway between the first and second stringer.
Add the stairs
Now, fix the 2" x 10" treads simply by nailing them down through the treads into the stringers. Nail the oriented strand board risers into the stringers. Your simple staircase is ready making it more attractive by painting it.