The only way to get a less-than-4-click level is with Mootilda's Grid-Adjuster.

In order for sims to use the space - it must be 16-clicks high. (Which is why your guy just stood inside the door.)

Ah, okay. And lowering the wall height on the upper floor obviously has some effect on the height of the ceiling on the ground floor. Well, now that I know, I can get on with it. I found the droopy eyelid thing on the archways pretty amusing.

The one other question I had concerned the act of leveling the wall height... unless it was a fairly small structure that I was working on, I had to build several out-structures, on multiple sides of the building, to be able to reach all points on the "roof". Have you found this to be the case also? The only reason it worked here was that I deleted the first ones I tried - maybe 7x7 squares, and started over with a much smaller structure, 3x5 I think. I wonder how it could be done with a dome that was far larger, say one that nearly filled a "huge" lot... like if I was making a sports stadium or something.