A large space concept is looking for ideas

Thank you for your encouraging words,

That's exactly how we want to do it. Keep many options open. And that is precisely the reason why we are thinking more and more about solid construction, especially because of the flexibility of the floor plan. However, what is now certain for us is the concrete basement. Most do not offer that, but want to build it with bricks. Since there was occasional concern about pressing hillside or groundwater on our property (the soil report ruled it out in the second examination but noted it), we don't want to take any risks there.

Now the only question remaining is how to find a suitable provider at all, or how to proceed best.

Normal construction companies. The ones that would build your stone house or just the garage. They pour floor slabs or retaining walls.

I would probably look for a general contractor who will build it massively including the basement; that would be mandatory for me. Trouble is inevitable and I wouldn’t know why the construction company shouldn’t build you a basement. For me, the part in the ground was poured by the construction company in concrete and the rest was built with masonry at the front. We also had slope and water risk, so a drainage was laid across the terrace, it's nothing complicated for a masonry company. I believe that if you largely know how your floor plan could basically work, you should simply start looking regionally for construction companies with a good reputation!! Then you will be wiser, I think, and in parallel ask one or two general contractors from nearby whether they could do it like THIS for you and how they would do it. I believe you could make progress this way, at least rule out some things. For example, I would only build with someone I get along with and who doesn’t try to impose their will on me. You need time and maybe in the end it will also work with an engaged young/old architect; step by step feeling your way, ups and downs but then it will work.

Then this shall be our plan. Thanks for that!

I roughly sketched a basement floor plan that gives us a bit more room to maneuver - of course, the upper floors would then be completely redesigned.

Just a layman’s question: Which construction companies are suitable for something like this? Google shows me either ones in the area that do landscaping or those specialized in large buildings/industry. Also smaller ones that only do civil engineering. So what should I best be looking for?

As I said, I am not one for floor plan design; I anyway think that someone with real expertise should handle it. You won't really get anywhere like this. The idea of the later, SEPARATE usage is not implemented in the picture.....planner/architect can do that. I like technology but in this case I would also rather trust the old ways and seek personal contact. Maybe ask at the municipality/neighboring municipalities, of course also google (good construction companies often have little time for websites), check new development areas....you will find a selection there. Reliability will be your most important companion, so I would take time for this search. This person will then also build it for you including the basement or may not want to give that part away at all. The more interfaces, the more risks, and your house is supposed to stand on the basement and not the swing.......I would never outsource that.

The basement is to be expanded at least in the front area towards the street as a living basement. We might even get involved ourselves here. The bedroom in the basement is problematic because the children are currently still small or babies. Of course, as long as the kids are small, they can move into a room in the basement with you. But even when they are a little older, I don’t necessarily want them to have to walk through the whole house in the dark if, for example, they have a nightmare at night h

What I would do: Plan so that the children will eventually live in the basement. For the first few years, they live upstairs and could easily share a room until school age anyway. At that age, they do much more than just sleep alone, and at 8, they are proud to have their own space. If you can bring yourself to do this, you can omit a shower bathroom upstairs, which frees up space. Either for bigger rooms or for a room for the washing machine. The kids will then hate it when they are 15 and still have to carry their stuff up two flights of stairs, but at that stage, they complain about other things anyway. Do you need two offices long term? If not, maybe just make one big children's room upstairs that later becomes an office for two. This leaves you a few square meters for a small seating area by the window where a person can quietly read a book later when the kids are in the basement. It would also give you flexibility; maybe after child 1 you think "one is enough!"