Procedure for constructing a new single-family house on an existing plot

Yes, exactly Kitchen is 3.31m wide and 3.54 high

Would not be my kitchen layout. Is it supposed to be like it's drawn there? Then there would be 60 cm on the right, 60 cm on the left, and 210 cm distance in the middle.

Why should it not be allowed? According to the development plan, I only know the 8m ridge height as the limiting height.

Here in BY this is certainly a deviation from the BY building regulations. Which building regulations apply to you?

Is the width of the kitchen enough for you?

We have a good 2.90m width, depth just under 4m, and put a U in there. The width is more than enough. But I would leave out the passage from the hallway; that really costs you meters in the kitchen.

Shower could be longer, closet in the bedroom planned individually under the slope. Bed under the slope. BUT: do not build a bathroom above the living area! Use common waste pipes of the bathrooms! Blue over blue! What else do you want as a trick from the architect?

I find the children's rooms too small. You have more space for sleeping and dressing than the kids have for their entire life. Children need space for playing, for friends, etc. 12 sqm is certainly possible, but in such a big house I would allow the kids more space.