Before construction started, Mike and I built a detailed model of the framing for the central core of the building. In particular, I was looking to make sure that all the vertical dimensions worked out they way I thought they would. The model includes the stairs from the basement to the first floor and the first floor to the second. We intended to come back and to the cupola stairs, too, but the real stairs got done first and came out very nicely, thank you.
What we discovered was that, yes, the vertical dimensions were about what we thought, but we also learned that some of the stacking of walls around the inside of the stairs were not what I had expected. Getting this right was a big deal as if we'd goofed that up in actual construction we could have had a big problem.
Viewed at though you are hanging from the living room ceiling. Really more like you're just above the plane of the ceiling but probably well outside the house ;-)
Shows the north side of the stair way. We didn't put in the door at the bottom as we decided to not use that space for mechanicals.
You can see some notes written on the cardboard flooring indicating things we needed to do differently when we build the real thing. We actually had the model out in the foundation with us while we built.