@DeanXeL , jepp, that´s mostly that, what I do too. Like I said, it sounds more complicated than it really is. Only difference is, that I construct those "halls" or "rooms" outside of the house in the size, they shall have, copy them over, then cut out the floor, and set the stairways. A lot in this game became more easy after me learning to think in terms of "rooms" instead of walls.
The same goes for wall applications like those things in the second frieze menu. They want to be placed from the floor above. And that is difficult, if there is no room, i.e. roof for example. Then I again use the room without walls, make a 1x1 piece, and fill all the space under a roof, that is not used as room. So the room in the attic stays like it is, and all the unused space there becomes another room. And voilá, now it´s possible to place the deco stuff to my likes. One can see that on my picture of the building with the mansard roof.
But it was a hard way to that point, cause I didn´t want to learn to build rooms, I tried to stick with the method of the previous games, drew walls and fences instead fo using the different room tools and change the look of the room borders later on. But since I always construct rooms, copy them and use the arrows to change their size, everything became a lot easier. Only to me this method is not intuitive... It´s still strange. :D
I mostly use not the platform tool for this but the x room, that is in the second line of the room menu. It also has no walls but constructs a full room, cause I realized, that the platforms merge with the surrounding room after they become the same floor height. This is not the case with the other tool.
But I use the platforms always, if I want to make a stairway through a foundation, cause we now are able to paint the walls of such a "foundation", cause it´s then part of a sunken platform. Here my example, the same house. The L-shaped platform is made for the basement stairs, and should be coloured after it is set. If the stair is built, the colours can get messe up and not fill the whole thing like they should. The other platform is for the partially walled stairs, that start in the ground floor. It´s only sad, that we cant use normal wallpapers in them. But I think, what I did, looks acceptable afterwards:
And cause I talked about the friezes: Here an example of friezes showing up in the staircase, but mostly invisible. But marking them, makes them yellow, and even the ones, that aren´t visible form above, will then show up. Shift and k is the right tool to then delete them one after another. And this is mostly, why I wrote, never to change an "exploded" room, after it is finished:
The small single white triangle is part of the upper floor and another room, so it is white, cuase we cant ppaint the ceiling like in TS3. That is a minor issue and can´t be changed, even after use of the trim tool, the lower part will stay white, unless we use a mod to change that. Such a mod exists but it changes all ceilings from white into one choosen appearance. No variations possible sadly.