Floor plan single-family house OWL approx. 150 sqm with east garden

You might need to internalize something: It is YOUR house. What your general contractor or we like is irrelevant as long as the thing doesn’t collapse.

What’s a bit unclear here: why do you need even more rooms now? What is supposed to be accommodated in the attic / basement?

Converting the basement to living standards will probably blow the budget. I thought you only needed more storage space and maybe a room as a workshop or something similar. For that, I wouldn’t have raised the ceilings or carried out mega excavations. How is the ceiling height in the basement planned?

2 rooms on the south side sound tempting, of course, if you already have a slope there and can install a window with two spade strokes. But always think about the costs. 2 more rooms mean heating, sockets, windows, windowsills, flooring, painting, etc. That can quickly get out of hand.
You can forget the fireplace cost-wise there, I think. But it’s only in the way anyway.

You might need to internalize something again: It is YOUR house. What your GU or we like is irrelevant, as long as the thing doesn't collapse. What is somewhat unclear here: why do you now need more rooms? What is supposed to be accommodated in the attic / basement?

Point 1: Everyone supports their opinions with reasonable arguments. We now have to decide for ourselves as laypersons how to weigh the arguments against each other. We are working on it! It's really a challenge. Point 2: Currently, we do not need any additional living spaces beyond those discussed so far. I am somewhat biased since a colleague of mine had twins with his second child after the house was just finished. I would like to have at least one room in reserve that I can convert into living space in the coming years/decades. Although one can certainly spend time/work/live well in rooms that would not qualify as living space according to DIN. At the moment, I tend more toward the basement. It's there anyway. It doesn't ruin upper floor layouts. It tends to be cooler in summer than the attic and can be heated (albeit possibly expensively). GU1 would have the basement within the thermal envelope, GU2 would not.

A roof is there for a reason.

I would always prefer a bedroom in the [DG] rather than in the basement.

Reasons;
- usually the [DG] is brighter or easier/cheaper to realize, so regarding light.
- I find it cozier/more homely

A roof is there too.

I would always prefer a bedroom in the attic over one in the basement.

Reasons;
- Usually, the attic is brighter or easier/cheaper to realize, regarding light.
- I find it cozier/more homely

The roof is already converted. The peak remains the peak and is much less suitable as living space than an insulated, heated basement room with straight walls and a light well facing the southern sun, which, due to the slope and the already existing basement, practically suggests itself.

Moreover, a staircase to the peak would strongly worsen the room layout in my opinion and make cost/benefit ridiculous.

However, I find the fear of triplets funny.

The roof is already converted. The tip remains the tip and is much less suitable as living space than an insulated, heated basement room with straight walls and a light well facing south, which is practically inevitable due to the slope and the already existing basement.

In addition, a staircase to the tip would, in my opinion, greatly worsen the space program and make cost/benefit absurd.

I find the fear of triplets funny, though.

Oh, so it's already fixed, sorry, then I take it back!!

Do not laugh at the fear of triplets. Someone wrote last year because the planned second child became child number 2 to 4. At the same time, friends wrote that the neighbors are selling because the second child became child number 2 to 4.

The attic is unsuitable as living space. We had that in one of our apartments. Okay for storage, but not otherwise. Here I would also prefer the basement room.