Floor plan 1.5 stories gable roof without basement - Criticism / Suggestions?

Yes, I was also warned about the wind corridor beforehand. I think I would close it off to the back with a glass door including a glass frame. Glass because otherwise I would immediately have a daylight problem again.

… which will be very expensive though. I now understand the thing with the roof :)

It might look nice (makes the living room visually a bit bigger), but in the end it’s impractical.

I rather think this slope looks like “trying but failing.” Anyway.
If you even out the corner, then you would have a good opportunity behind the door in the office to put cupboards, which can serve as storage space, e.g. also for summer/winter clothes. I will come back to that in more detail!

Based on relatively current offers – depending on own work 440,000 - 500,000€ including land

What kind of offers are these? What do these offers include? How expensive is the land? What amount of incidental construction costs are you expecting?
I see, even though I can only guess the land price, not even the massive double garage with insulated finished attic is included.

It is certainly somewhat unorthodox. Above the door would be the 12th step, with a step height of 18.2cm -> 218.4cm from finished floor level (admittedly: upper edge of step).
Shouldn’t at least a 2m high door fit underneath there?

I don’t think so. I also consider your stairwell to already be too short. And whether you have to duck your head under the overbuilt stair might possibly be explained to you by .

The study should possibly be used as a master bedroom in old age.

I missed that.

The basic idea here was maybe to separate the ground floor from the upper floor later on. Then of course the ground floor shower bathroom should not be located in the entrance area.

The shower toilet is not age-appropriate.

Regarding the cloakroom, I had briefly considered giving the utility room a 60cm "cut" in favor of the entrance area. To be able to "install" a roughly 1.5m wide cloakroom there. However, I also think the nearly 11m² utility room is needed, with central ventilation system, washing machine and dryer.

Can you get more specific here?

I will take this request for general points:
You are planning a roughly 160 sqm house, which will cost about 400,000€, plus incidental construction costs and usual additional costs like outdoor facilities. In addition, you plan a double garage, which is not cheap prefabricated, but massive with developed attic. Additionally with a roof over the entrance to the house, which simply makes it dark. The roof above must be extensively sealed to the actual house. Energetically it must therefore work with the garage (also a cost factor). All of this just to create additional storage space, although your roof will get a nice attic.
The expensive fun of having only attic stories everywhere has additional disadvantages:
The hallway on the ground floor is dark, the hallway on the upper floor stretches in length and does not become more charming by that, especially if such artificial light is constantly on. The bathroom does not get a proper window at all. These would be major drawbacks for me. Also the wasted space of the long hallway – 3 sqm could go to the bathroom. In addition, it is planned for later to operate this upper floor as a separate living unit. Without balcony and a rather small kitchen, you won’t see the most demanding tenants above you now.
Meanwhile, you want to be happy in your small shower bathroom.
Since the money is not enough for a jack-of-all-trades solution, I would focus on your current wishes in your position.
Regarding storage space, a nice fixed staircase can be positioned over the actual stairs and the attic used. Elderly can also later create a hobby room there. The attic space is there anyway.
I also consider it risky if you plan minimum dimensions yourself (toilet, toilet door, stairs, roof passage, upper floor windows).
Sanitary walls are missing, window lintels are not planned, and RBM (rough building measurements) are not the mason’s manufacturing sizes as a finished product.

I consider the bathroom on the upper floor too small as a family bathroom for 5 people. Then two doors in it – privacy is no longer available. You are not just two!
The dressing room is only half as useful because the kitchen space (KS) is also there. I personally advise rather generating the slope as an 80cm deep wardrobe room. Schwörerhaus has it with sliding doors in the show house in Helmstorf.
I already mentioned the rest in the first post.
Also the living room corner, which must here serve as an all-round TV and passage to the terrace, is not the quiet zone as imagined with 5 children.

Here are some points that are not necessarily from me but should always be considered:
Concerns that teenagers sometimes take over the kitchen in the evening with friends or the terrace roof in the off-season.
Consideration whether the teenager (who will be 17 or 18 at move-in) should get the lower room.
Sliding doors are not easy to operate.
The mentioned passersby are your neighbors, against whom you can also shield yourself with a hedge.
Childcare should be manageable from the kitchen/garden.

I recommend an architect for an adequate redesign or a general contractor, to optimize a standard house according to size and orientation.
Playing is allowed, but mostly it will not be built anyway.

Is there an architect's standard manual somewhere that states that approximately €500,000 should always be assumed? I have now seen in several threads that €500,000 is always assumed...

Is there an architect standard manual somewhere that states that approximately €500,000 should always be assumed? I have now seen in several threads that it is always assumed to be €500,000...

Is that so? I can explain it by either looking at a certain price range (catalog price) without considering additional costs and without consulting a professional. Or that someone inquiries somewhere, and the general contractor roughly estimates a standard house flat-rate based on their model houses, here a gable roof, single-story, about 160 sqm. The mentioned garage and mega canopy are either not discussed at all or the topic is deferred by the general contractor for later. Hopefully, the original poster will enlighten us.

Is that so? I can explain it as either looking at a certain price range (catalog price) without considering the additional costs and without a conversation with a professional. Or that someone inquires somewhere, and the general contractor estimates a standard house flat-rate based on their model houses, here a gable roof, single-story, approx. 160 sqm. The mentioned garage and mega canopy are either not talked about at all or the topic is pushed aside by the general contractor for later. Hopefully, the OP will clarify for us.

Well, we recently talked about a house with 220 sqm where the architect also set 500,000 € and that was the OP’s price limit. As a builder, one should always keep in mind that an architect’s cost estimate is rarely accurate.

As a client, one should always keep in mind that an architect's cost estimate is rarely accurate.

That's how it is. I don't want to remember numbers on vacation, so I'm not paying much attention right now. I'm reading in bright sunshine :D

Is there somewhere an architect's standard manual that states that approximately €500,000 should always be assumed? I have seen this mentioned in several threads, where €500,000 is always assumed...

As a client, one should always keep in mind that an architect's cost estimate is rarely accurate.

I do not think that a universal answer like "42" would be found in Neufert, although of course I do not know all the editions ;-)
The popular amateur cook Dr. Alfred Biolek, may he rest in peace, used to say "iudex non calculat," which apparently also applies to design artists. The more designer-like the architect, the more he probably scorns the mundane numbers and prefers to leave that to the civil engineers.