Floor plan: New construction on existing bungalow basement, 1.5-story

I would plan something like that.

I can already see the children's rooms with an open roof structure and a cool loft bed up there. :) The 13 sqm will quickly become more than 20 sqm.

The manufacturer can also "imagine" that and has both building materials in the program.

The construction manager at least said that "his" companies can process both types of bricks well.

I would plan something like that. In my opinion, the roof truss can be completely reused. These are all prefabricated elements.

Such an offset shed roof is probably a bit too modern for our eyes, but it would certainly be a sustainable construction method. The roof truss (individual rafters, purlins, battens, I assume?) will then be temporarily stored by the carpenter between dismantling and rebuilding? The current roof has no insulation and no middle purlins (I showed a picture from inside in post #27). Do individual components have to be replaced or reinforced here for overlay insulation, photovoltaics, etc.? Has anyone here done this before?

I already see the children's rooms with an open roof truss and a cool loft bed up there. :) That makes the 13sqm more than 20sqm right away.

Yes, we also think that’s a nice idea. A partially open roof truss (and reducing the attic about 1/3, but still making it usable) we have also discussed. That would also be possible with the gable roof.

Such a staggered shed roof is probably a bit too modern for our eyes, but it would certainly be a sustainable construction method. The roof truss (individual rafters, purlins, battens, I assume?) will then be temporarily stored with the carpenter between the deconstruction and new construction?
The current roof has no insulation and no collar beams (I showed a picture from the inside in post #27). Do individual components need to be replaced or reinforced here for insulation above the rafters, photovoltaics, etc.?
Has anyone here done this before?

The roof truss consists of elements that can be completely reused. I do not find the existing roof truss suitable for insulation above the rafters. I assume the rafters have a cross-section of 8cm*20cm, so insulation between the rafters is advisable, possibly additional insulation above the rafters.

Temporary storage on the construction site saves transport and storage costs.

The construction manager at least said that "his" companies can process both types of stone well.

For me, both stone and wood are still in the running.

Such a staggered shed roof is probably a bit too modern for our eyes, but it would certainly be a sustainable way of building. The roof structure (individual rafters, purlins, battens, I assume?) will then be temporarily stored at the timber builder’s place between deconstruction and reconstruction? The current roof has no insulation and no middle purlins (I showed a picture from the inside in post #27). Do individual components need to be replaced or reinforced here for sarking insulation, photovoltaics, etc.? Has anyone done this here before?

This was often done in the past, with some roofs still perfectly stable today, last rebuilt in Mozart’s lifetime and with individual beams replaced during the imperial era. Except for the rarely reinstalled battens, your assumptions are correct. Currently without middle purlins is good, as this might allow more flexible planning for possibly added middle purlins. I am a fan of the concept of fully covering one gable or shed side with appropriate systems rather than putting things like roof racks on top. In my view, the suspended solution has its justification for retrofits and partial coverings, and otherwise is the second choice.

The squirrel feeds itself with difficulty...
After some back and forth (including involvement of the structural engineer and change of architect), there is an update on the floor plan.
In the floor plans, south is always at the top.

Changes compared to the last version (from top to bottom):

[*]Knee wall raised to 1m
[*]No more "setback" balcony. Balcony aligns flush with the gable wall (1.50m depth)
[*]Parents' bedroom with wardrobe area
[*]Enlargement of the ground floor hallway (due to enlarged cantilever slab at basement ceiling)
[*]Additional support in the kitchen
[*]Removal of one of two terraces

What is still not satisfactory:

[*]Child 3 room too narrow
[*]Bedroom too large (option: move wall to the right in favor of Child 1 according to plan)
[*]Dormer window not centered in dormer

What is still to come:

[*]Separation of living area (e.g. sliding door)
[*]Bathroom and/or Child 3 with high ceilings up to the roof

Currently, the structural engineer is calculating everything, next the whole thing will go to the energy consultant before the building application is to be submitted shortly thereafter.
Are there any suggestions / additions / criticism from the forum community?

No more "recessed" balcony. Balcony is flush with gable wall (1.50m depth)

The question marks behind this balcony as such do not change that.

Bedroom too large (option: move wall to the right on the plan in favor of Child 1)

And the wall between K2 and K1 along with it, in the ring exchange the wall between K3 and K2 also shifts.

Dormer window not centered in dormer

Not decisive for the outcome and without moral value. I would omit the wall between stairs and built-in shelf.