Thanks for the response!

At one time I did try that, but then I was left with a hole in the middle. ;}

I created a small circle in the same plane as the upper floor, and then in the lower floor. I selected the inside edge and the inside circle, then lofted. As near as I can tell, it did the right thing, with the exception of the circle in the middle.

Did the same for the bottom, and it looks good.

Is there a better way? The docs seemed to say I could take the inner perimeter (which is non-planar), and then draw another straight line and boolean form them into a floor. But I couldn't make that work...
I guess it only works for planar, and not organic?

Thanks!

Jason