1) create poly cube.
2) Scale X: 4
4) Check "Smart Transform" then click "duplicate"
5) snap (hold down x) new cube to Translate Y and Z to 1.
6) WITHOUT clicking anything else, press Ctrl d and a third cube will appear at translate Y and Z at 2. Press Ctrl d again and another cube will appear at translate 3, and so on and so forth for however many steps you want.
This same technique can be used with other types of stairs as well. If you wanted to do a spiral stair case, I would model a step first, then move it far from the grid center, then move the pivot opint to 0,0,0 and do the Smart Transform duplicate I explained above to make all the stairs you need. All you have to do is copy the first step you modeled once, move up a little and rotate it as needed, then Ctrl d it a few times.
Hope this helps.