Floor plan design and garage roofing

Then fill out the questionnaire completely

Draw all existing or desired furniture to scale. Consider the movement space.

Bottleneck wardrobe, WC, 2 entrance doors. Remove the one to the garage. This greatly relaxes the corner. Check the measurements, the cabinets look like dollhouse furniture.
Shower in the utility room?
2 doors to the bathroom, one too many.
Hard to write anything without knowing you or knowing your preferences. Something doesn't please you, otherwise you wouldn't write here.

Our wishes are actually only,
- straight staircase
- 3 children's rooms
- no basement
- open living area + kitchen
- direct access from bedroom to bathroom

The 3 children's rooms are probably less a wish than a necessary need. A basement would cause significant additional costs.
An en suite bathroom is nice if there is sufficient bathroom/WC available elsewhere, otherwise rather a gimmick.
Is there a budget or maximum freedom?

In the entrance area with the collection of doors makes little sense.
I understand if someone likes a straight staircase (Pinterest etc.), but then it must also stand on its own as a structure in the room and in design. Here it would stand in a narrow hallway and underneath would be the utility room. I would look for a nice and fitting floor plan for me or first have a design made exactly for that before spoiling the rest with a special wish staircase or other shaping areas.
I am curious how the architect will design the corner stub in the kitchen, also the "pantry" a) is usually not very useful and here b) not a pantry. Please measure its size.
What happens with the sports field area between the kitchen counter and dining table, there is nothing but wasted, expensive space.
Do you actually have such a sofa and should it also stand completely like that in front of the window front?
Any other furniture there?
As already mentioned, consistent and correct furnishing of the rooms is absolutely necessary.
Utility room + heating room over 17 sqm, too much dead space in the middle or what is supposed to happen in there? Is that a shower in the corner?
Upper floor: Then understandably the air runs out because if you want an en suite bathroom, the kids also need one, respectively a shower/WC for three.
As it is, two doors in the bathroom, often seen situation, which in my opinion is an absolute planning failure or you have to hide something else with it (here e.g. en suite removed from the wish list). Also, the door opening inward into the dressing room... the bathtub as a posh design piece in the middle of the room, and a slalom to the WC in the dark box. Almost 15 sqm for a bathroom is huge and consumes space without significant added value.
In children's room 1 I wonder if the occupant is supposed to practice archery because of the length.
No criticism of you, but of the draftsman; I do not want to use the term "planner" here.
Therefore my opinion: back to square one, determine real needs, away from staircase or house shapes and simply find the suitable floor plan. Once that is there, a nice facade will also be found. I think a rectangle might also suit better here.

What do you think of this plan?

Distance.

would that be possible, what do you think this would additionally cost to use it as a hobby room and office, because unfortunately I am missing all that in the current planning?

In children's room 1 I wonder if the occupant is supposed to practice archery because of the length. No criticism of you, but of the drafter; I don't want to use the term "planner" here. Therefore my opinion: Back to square one, determine the real needs, move away from stairs or house shapes and simply find the appropriate floor plan. Once that is found, a nice facade will follow. I think that here too, a rectangle might fit better.

Well, child 1 was probably not a wanted child, and all three children are less important than the staircase being a straight shot. I suspect the planner is too strongly infiltrated with specifications. The drawings look like a planning that is already far too detailed. However, a design plan should always be based first on a preliminary design plan*. If this is already so far from the desired room program, there were essential omissions. However, details seem to be planned, even though much is not recognizable due to illegibility (and the not fully shown plot including neighbors). It has already been decided that the chimney will be a backloader (?) – please do not answer, but back to the beginning! *) and actually also take a rest period in between and carry out the key decisions

I am always amazed that people who already have children - and in this case even three - approve of such children's rooms. They are always furnished like airport hotel rooms. But probably other people will soon say again that 6 square meters used to be enough and one was happy with that.
Our two boys each have an 80 x 140 desk with swivel chair, a 100 x 200 cm bed with a small nightstand, a Billy bookshelf, a 4 x 2 kallax for LEGO and other building sets, a rolling container for writing and painting supplies, a chest for stuffed animals and a Pax as a wardrobe. Additionally, wall shelves for the Tonies and odds and ends and pictures. The older one also has a hanging chair where he likes to read and an aquarium. The younger one also has a dog bed. That is their living space, until they move out, at 14 sqm. I wouldn’t know how to fit all that in the rooms with the layout in this plan.

I am always amazed that people who already have children - and in this case even three - approve of such children's rooms. They are always furnished like airport hotel rooms. But probably other people will immediately say here again that 6 square meters used to be enough and one was happy with that.

What bothers me "only" here is the lovelessness and especially with K1 also the tube shape of the room. With three children, usually at least the oldest is intellectually capable of having a say as a stakeholder in the planning process.