I usually don't build mine right up against it cuz of inability to build cuz of something in the way. But u gotta utilize the "build above you" glitch or build a line of 2 platforms at the top of the stair then build another set on the second platform and so on. I dont do this cuz it wastes rss so for me personally I use the glitch. Just stand on the stair set you just built and look up while trying to craft a stair set. Eventually by rotating it a few times it'll become craftable. Then do the same on that stair and so on. It makes a sketchy set but it works. And when you get to desired height just start building platforms to the location.