Ground floor approx. 100 sqm, upper floor expandable (planned bathroom, 2 children's rooms, 1 storage room)

Nordlys then we call the whole thing suboptimally planned and built. For example, having breakfast on the terrace becomes a marathon when you have to get everything from the kitchen, ...

This house is whole and not small, but since everything is first squeezed downstairs and the upper floor is not included in the planning, it's simply impractical.

I still have an idea for the upper floor with as little hallway as possible. What is still space in the rooms? Definitely, good stair lighting is needed.

One more point. If the beams rest on the top edge of the window, then the upper floor will be quite low. What height is required for living space in SH?

I have another idea for the upper floor with as little hallway as possible. What else fits in the rooms? A good stair lighting is definitely needed.

Very good! If you could make the stairs a bit steeper and thus shorter and shift the whole thing towards the entrance, much would be gained.

One more point. If the beams rest on the top edge of the windows, then the upper floor will be quite low. What height is required for living space in SH?

I have also been wondering whether the upper floor even qualifies as living space. And if not, what exactly the general contractor means here by "convertible attic." I would like to see the contract for that.

I am 61 years old and have never had breakfast on the terrace and I won’t do it either. It’s way too windy for that here. - And if I carry something out, I use the back door for that. That’s what it’s for.
Carrying food into the living room. Why. There is a table and a corner bench in the kitchen, that’s where you eat.
Bedroom too cramped... well, it’s not a gym, but it’s just about okay.
Only doors leading into the hallway I accept. Otherwise: It wouldn’t be my house, but it might suit the two of them. - No one cares about ceiling height upstairs if you do it later. It will have standing height.

I actually find much more striking what the general contractor or architect (can you even still call them that?) delivers here. Built as ordered – not a hint of brains invested or the customer advised.

However

The OP wants upstairs 2 children's rooms, bedroom, bathroom and storage.

No, that won't work.

I have another idea for the upper floor with as little hallway as possible. What still fits in the rooms? Definitely need good staircase lighting.

That also won't work. You run into the slopes. (But if necessary still feasible with different door placement)

I took a look: downstairs the living room width is 3.76... that would be the depth you have in front of the stairs as room space if you cut off one meter as a hallway. Looking at the windows upstairs


I see about 4 meters in width at 2-meter standing height. Then we would have about 15 sqm in the front area plus the space under the roof, where you can't even put a bed. Divided by two children’s rooms, that’s 7.5 sqm per child. Each child could get a niche extension, but that doesn’t count as living space. So they would have less than the size of a cell. In the middle you now have to subtract the width of the hallway and stairs. Roughly 3 meters remain for a bedroom, which realistically only has a one-meter-wide standing strip in length. If you get rid of the bed frame and can sleep on a futon mattress, that would work... but a bed won’t fit under the sloping roof. And the fact that it’s then not even official living space adds to the problem.