Theoretical stair design (C) Daniel Friedman . can purchase pre-cut stair treads of the proper width but it& 39;s certainly trivial to cut your own as well. If your deck stairs will use closed risers you& 39;ll need treated 2x lumber to cut those as well. . Because if you don& 39;t it& 39;s unlikely that your stair tread cut run and rise markings will be .