Stepped surface

I asked last week how to get raised text or shapes protruding from a
curved surface and I got some excellent replies. Now I find What I
need is to "step" the offset surface to different elevations.
To explain, let's say that the original curve is a sphere and the
first offset shape is a rectangle. This produces a rectangle shape
offset from the sphere by a specified height. The surface of the
rectangle is curved to match the sphere. Which is what I need but I
also need to "step" this curved surface.
I can do this to some extent by offsetting (expand) the rectangle
surface with a smaller SQUARE (or other) shape. But the square must be
completely inside the perimeter of the rectangle or it fails. And I
need to step right from, at least, one of the edges. If it touches or
overlaps an edge, it fails.
Is there a method to do this.
Thanks Peter