City villa 160-170 m², issue with connection of windbreak to garage

hm .... hmm ... you really don't know how to start.

[*]Garage
how are the bikes supposed to get into the bike storage area?
[*]"Vestibule" and hallway ... cloakroom space? There is no place for 60 cm deep cabinets, ok, under the stairs ... but why the vestibule? Why not just a canopy or something, then the bikes could be pushed into the garage extension as well.

[*]Kitchen 17 sqm .. but work surface like in a 6 sqm kitchen, why does the terrace door on the garage side still have to be on the left wall for example?
Table in the kitchen stands in the passage to the dining room.
[*]Living area .. sofa directly in front of the floor-to-ceiling window ... why?

[*]Guest/workroom has exactly the same sqm as the two children's rooms combined. 275 cm .. my god, a 140 cm youth bed there and barely any space next to it.
[*]Parents almost 24 sqm .. but unfavorable window positioning in the dressing room, therefore no two continuous rows of wardrobes possible, entrance to the sleeping area next to the headboard of the bed
[*]14 sqm bathroom and right at the entrance a bottleneck caused by privacy walls

Thoughts on a 1 to 2 m house extension .. the budget might get tight then.

I haven't found anything about that now, but are there really 3 children planned? If not, I think 2x guest or workspaces are a waste of space. It would also noticeably ease the situation upstairs.

In many points, I can only agree with kbt.

Children's rooms are terribly narrow. I would plan at least 3 m there.
A window in the dressing room destroys your possibility of generous furnishing.
I find the headboard next to the door very uncomfortable.
Bathroom larger than children's room. I don't understand something like that.
I would open the kitchen to the dining area and save myself a second dining space. Then turn the table 90 degrees, that will give a bit more space.
I would change the kitchen so that I can place a two-liner with a peninsula. (So cancel the small terrace door to the garage and divide the long window front to the garden so that a peninsula can be placed.)
Really think about where the wardrobe should go.

And what does the general contractor charge for the design? Your change requests are at least 20 sqm more. That will cost a lot.

If the car is really a left-hand drive parked forwards, the passage to the bicycles is on the wrong side and so is the one to the house. Or, with the car parked backwards, the gate is too narrow, even for non-blonde men. Nordkind and guest I would swap. Two guest rooms, two dining areas: I would rather clarify the concept at this point than add a meter to the house.

On the other hand, only two full floors are allowed. How large could a roof extension be in this hypothetical scenario to avoid problems with the building permit?

A roof extension will not become a full floor here.
Is the maximum house height defined?

Could one realistically create one or two usable rooms considering the roof slopes and the floor area?

You can draw that yourself if you sketch the cross-section on graph paper.

I would first tidy up the ground floor.
The windbreak is completely unnecessary as a windbreak.
Either it is incorporated into the garage or it remains within the thermal envelope and becomes the utility room.
As it is now, it is just an unnecessary cost driver.
Same for the kitchen. Kerstin has already listed everything.
I had more kitchen units in my rental apartment and also in the terraced house. Allocating 17 sqm for the kitchen is more than decadent, at least for the indicated "use."
Enlarging the house smooths out lousy floor plans but pulls financing down.
My suggestion:
Convert the utility room into this windbreak. Then move it back.
The entrance is the entrance. In the NE-O guest room and WC, then the E-W remains for the main room.

Bring the bathroom on the upper floor to a normal 10 sqm.
Extending the stair wall brings more disadvantages than benefits.

We have taken another step forward in the planning and have partially incorporated your comments into the floor plan. The vestibule has been dropped for now. Regarding the garage, a continuous roof connection to the house is still under consideration. We'll see. Some small details are still not quite right, e.g., window sizes. But that should be resolved in the next few days. As always, comments are welcome.

The living room door will always be in the way, when it is open you can hardly get between the dining table and the couch. Personally, I also find the living space too small to place the TV as a room divider.

Best regards
Sabine