This uses the segmented nature of Sketchup geometry to make a set of curved stairs, or a full spiral if you want. You also get to see that I don't always get it right the first time.
Note the use of shift select to deselect the arcs so the long edges can be welded which allows them to move together.
I've used a 96 segment circle and split it into 3 segments per stair which gives a fairly smooth curve for 24 stairs, increase or decrease to adjust the number of stairs in a full rotation.