When you view the interior of a building (also while designing), I think it should be possible to hide floors above a certain one that you’re interested in looking at. As it is, it’s very difficult to place items in a floor below the top one, and you have to be very finicky with the mouse and camera. Note my struggles in the attached video at 3:50.
IIRC, the slice view used to do this at one point, but it doesn’t any more.
I tried that in this playthrough, and it certainly doesn’t now. I don’t know about before.
This would be very helpful for multi floor layouts