Improve floor plan - how?!

That’s how it seems to us too, that something is not right here.

Who chose this unsuitable base model to tinker your wishes into it?

Everything else still sucks.

So the simplest and best solution would be to rotate the roof again, am I right?

Everything else can only be fixed by choosing a suitable base model. Rotating the roof doesn’t help.

Who chose this unsuitable base model to patch your wishes into it?

The consultant of the developer. But the architect also did not point out any problem to us.

Everything else can only be fixed by choosing a suitable base model. Rotating the roof won't help.

:'(

The consultant of the property developer. But the architect also did not point out any problem to us.

I suspect you mean: "consultant" = sales representative; "property developer" = general contractor (he is only called property developer if you buy the house along with the land from him); "architect" = draftsman who incorporates your wishes and depicts them visually. As a layperson, you are obviously pretty stuck when dealing with such a collection of "professionals." So you have to educate yourself about certain basics. From your inquiry / idea of remedy with turning the roof, I gather that you could only partially follow my explanation. Therefore, I say it again in other words: for a pitched roof house with a high knee wall (however, we should discuss whether this is the most suitable way here), you can only start with a pitched roof house as a base design – ideally with the same, less, or no knee wall. Choosing a "city villa" and pulling the roofline lower over its face is not suitable – regardless of the ridge direction. You need a different base design (with a pitched roof floor, which some providers call "country house" – don’t worry, the Forsthaus Falkenau is not meant, the style can be "urban-modern"). Usually, you are also best off with "rectangular" rather than square floor plans. You don’t even need to try to improve the shown design; that will only lead to frustration.

I am making every effort to follow and do think that I understand. However, I must admit I am a bit overwhelmed and do not know spontaneously how to solve this.

A different question: do exterior roller shutters even make sense in a low-energy house?

Choose another base from their catalog or use a different provider. The house shown suggests that you need to save money: then forget KfW40 / low energy, because unfortunately the payback period is especially low there. External roller shutters in a new build? - no, right?

.. I also do not consider the draft to be sensible, but I do consider roller shutters appropriate. And never plan without external shading options (except in the north), that would be madness for the summer half-year.