We are goind to built a stair like this one:
But instead of two "floating" stringers, since ours will be against a wall, I thought about using plate steel and making it more flush with the wall. The fabrication is simple enough, angle iron for supports welded to the plate steel. The stringer will the be affixed at 4 points along the wall (1.5 meter intervals) like the sketch below:
I was thinking about using 1/8" or 1/4" plate but I'm not really sure how much plate steel could move or be "springy" in this situation. How thick should I go?