@Metaphasic , there is no need for elevators, only sometimes one needs to be very, veeery patient... I needed roundbaout 3 hours for this staircase, cause of the phenomen, that a few people here descibed as "exploded room". One time I´ve got invisible friezes inside, then I lost the colour of the wall through the foundation, then a stairway won´t be placeable anymore... Such things are annoying, and it´s only, cause this game is so buggy.
But hey, we all know that, and mostly everything can be solved, simply by doing it again and again. And leaving a lot and reloading it sometimes solves such issues as well. Don´t ask me why, but it does.
Here a few pictures of that particular house and it´s staircase (it´s still work in progress):
And the stairs from the attic to the basement:
The ground floor area:
It´s possible to see, that there is a small glitch with the walls of the stairs, that lead to the basement, a small white stripe, and I can´t avoid this showing up. That´s annoying but it´s a minor issue in my humble view. And on the first picture you can see parts of my prepared "rooms" and "platforms", that I then later used to create the single rooms for the open spaces and the partially walled stairs in the ground floor area.
Btw I am not sure, what to do with that building. It´s part of a quarter, where I built a few mostly Early French inspired mansions. But it is so huge, and the lot is small in size compared to that building. I thought about making a museum or an art gallery but at the moment the whole thing is abandoned.