Assymmetrical Sprial

I am trying to build a script for a spiraling elliptical stair. I'd like to rationalize it so all of the curves are arcs or ellipses.

I am also trying to create a landing that transitions/blends into the second level opening (which is a true ellipse.)

The widths of the stairs (for now) remain constant at 5' wide

Any help to get started would be great.