Single-family house (2 floors + residential basement + developed attic) approximately 200 sqm - changes

Yes and no.
There are massive stairs from the basement (~2.25), to the ground floor (~2.625) and then the attic (~2.50 without slopes). Then a wooden beam ceiling, and the roof starts on top of that. There is a massive staircase leading to this floor.
I want to build the roof peak itself as a wooden platform into the roof (underneath ~2.35). But of course, only space-saving stairs lead up there. Whether a bed or a chill or play area comes up there, the children can decide. The figures in brackets are the clear structural heights.

This is completely confusing again. This is your division, if I understand you correctly (from bottom to top):

1. Basement
2. Ground floor
3. Upper floor
4. Attic
5. Roof peak

And the question was, where is the drawing for the roof peak, because I only see 1-4.
What is a wooden platform as a roof peak? Do you have a picture or a sketch?

No. Nothing has changed on the floors.

[*]Basement
[*]Ground floor
[*]Attic floor (but built with 250cm walls, so without roof slopes. Then wooden beam ceiling. Then the 50-degree roof begins. Inside it is the floor/roof peak – suitable for installing a wooden floor/platform, but there are no plans for that)
[*]Roof space

The stairs lead up to the roof space

I’m open to using different terms if someone tells me what the things are called. So far, I’ve always called the attic floor the upper floor because it is a full storey (250cm + ceiling or 150cm knee wall). Then the knee wall discussion came up and now I’m very confused about the correct terms.
In short: There are 3 fully built floors: basement, ground floor, attic floor. On top of that a wooden beam ceiling and then the roof with 50 degrees which houses the roof space.

Honestly, I think you don't even know what you want yourself. Look here:

[ATTACH alt="Etagen.jpg" type="full"]39424[/ATTACH]
That would be 5 floors. From #79 onwards, I suspect that the attic won't be developed and is only accessible via a space-saving staircase (please mark it). Or does he mean in the end just a foldable attic ladder? What exactly now? The plans are missing the attic anyway.

No, we just have problems understanding each other, which is certainly due to my amateurish language. Thank you for the illustration, with it I can hopefully describe it: EDIT: (from bottom to top) Basement (comes underground or definitely lower) Ground floor I have now gotten into the habit of calling the first floor Attic (roof/pitched) floor The thing at the very top is only for me to calculate how much space would be created if I were to add an intermediate level there myself. Please understand it as a kind of loft bed. With a height of 2.35m underneath, there are still about 6sqm with over 2m room height. The children can use that well for playing/sleeping/chilling. possibly the model railway.... Edit: Since this is firmly planned, we would also think of lighting up there and that is why I simply put 2 windows there and in my program quasi as an extra floor. Of course, it is not. Ideas for lighting in the gable would be of great interest to me.

I have now gotten into the habit of calling the attic OG

Your OG is not directly under the roof. That only comes above it. So it is not an attic.

The thing at the very top is just for me to calculate how much space would be created if I were to add an intermediate floor there myself. Please understand it as a kind of loft bed.

Had you mentioned that somewhere already? Not entirely unimportant, that point, right? How do you get up there? What is supposed to happen with it until you have built the intermediate floor (DIY - I’ll add the list from #31 in my head then)? If you want to walk on it, there has to be a walkable ceiling in it. Just hanging it up and putting insulation on it won’t work then. Are you a carpenter?