Use this procedure to generate a polyline from the edge of a stair. The polyline is generated at the stair bottom elevation.
You can keep some sample polylines in the drawing, and use the final choice to project to. That way, you can project the stair edge, edit the stair, and then generate the polyline, change the stair again, generate another polyline, change the stair again, and, finally, project to the best version you created.
Generating a polyline from a stair edge
A polyline is created at the stair bottom elevation along the length of the stair run.