Single-family house (2 floors + residential basement + developed attic) approximately 200 sqm - changes

Maybe house 2m longer for that?

Longer to the right according to the plan? What is important to us: all changes must then be checked to ensure they are cost-neutral compared to the current design. We cannot/will not risk more than the current 450k maximum (that would be with a residential basement and heating in the basement, clay plaster and attic without roof slopes). I would feel better if we only end up at 410k (without residential basement), since it has already been established that it will be more expensive anyway.

The dimensions of the staircase including floor height are sufficient for us to assess the matter. The presentation hardly matters.
Outbuildings are the ideal bicycle parking space - car next to it - is that possible far south?

The more floors you build, the more expensive the thing gets just because of all the load-bearing ceilings. Therefore, I would extend the house to the south and try to do without one floor. For that, I would include the garden landscaping costs. Unless there are exactly 3m foundation blocks in front of the existing structure, the excavator will tear that away on the first day and dispose of it along with the excavation.

If it were mine, it would probably be a 2.5-story building on a slab foundation measuring about 11.5m x 9m (exact plot dimensions would not be unimportant here). But it also depends on the foundation effort. Whether the basement is really worth it must be calculated precisely. We are currently seeing this with . He gave up the basement, even though it was offered due to height differences. Still, the slab foundation was significantly cheaper.

There is no development plan here. So everything can be applied for. In an informal preliminary discussion, we were pointed out the 3m to the neighboring property, zzz the note that since it is already built on the boundary to the left and above and on the left there is only a parking lot that probably cannot be redeveloped for residential purposes (8m wide strip), one could talk about an extension of the building 9m in length. In addition, we were immediately pointed out the existing setbacks of the residential buildings of 6m to both streets (plan below and right).

The gable faces east and west. Extending the house to the south significantly reduces the sunny garden (in winter, about 2/3 of the property is shaded during the day at any time). And doesn't it look strange when you stretch the gable side like that without increasing the width?

I think there is no development plan?! So the gable can face whichever way it wants, right? And it's clear that your garden will be lost. That's why I was talking about freeing the areas in front of the extension from concrete. Apart from that, building a tower for 2 meters more garden is, in my opinion, completely crazy in this case. A house is not a paint trial that you quickly erase and start over later. You want to live there and possibly have to sell it someday. 5 stories in the residential tower – no one wants that – not even you.