What is the end use? Are you planning on getting this actually made, or does it just need to look right?
A quick way would be to use the interpolatecrv command and trace the profile of the risers as they go up. Then extrude the resulting curve vertically by desired amount.
On a side note, generally you’d do this sort of stair with basically straight risers and then winders at the corners, at least in my area.
Hmm yeah that looks a bit tricky because the stairs are pretty free form. I’ve had to do something similar in the past, started with interpcrv (played around with the setting to try get a better ‘fit’ to the plan), then extrude to approximate height, then turn points on for the surface and manually pull points up and down using the gumball to get a pleasing line.
If someone has a better method, I’d love to hear it also!
A quick screen grab of interp crv below. This version deviates from the stair in plan a bit too much though, would need work.