I assumed he meant a helix shape, but that is commonly referred to as a spiral stairway.
One idea would be to partially cut bar sections from a plate at the appropriate angle, then roll the plate, then finish cutting the sections out.
In the past, with double stringer spiral stairs using flat bar similar to that, they were assembled by using unrolled bars, punching or drilling holes at the appropriate locations for bolted stair treads, then bolting them to the stair treads would pull them into shape. This was on a relatively large radius, not a tight spiral as you might see in a home stairway.