New single-family house in southern Germany

3,000 € per sqm just for the house? Or all in? Just for the house seems to me to be the Bodensee bonus?

I definitely cannot imagine building completely without storage space.

That wouldn’t make sense for anyone.
Nevertheless, there is a considerable range in the interpretation of this term and what one "needs."

I would always build with a basement, but then use it sensibly.

SENSIBLY.......so far so good, but just as an example......

So in the new build for my children, a large party room, a guest bedroom and a hobby room are planned in the basement, and of course the utility room (HAR), plus there are 2 storage rooms and 1 WC. Garden tools and bikes won’t go in there since we built without a basement exit. They have to go into the garden house or garage.

.......the general question would arise for ME whether I want/can spend tens of thousands of euros on an extra "party room," when I am building a nice, new house with stylish living spaces.....and then also for the kids!!! Of course, that’s none of my business, but you have to be able to afford it. Whether children, besides their own room, often their own bathroom, also need their own party room in the house....hm. I wonder if Papa’s subconscious hunter & gatherer is coming through and he just wants maximum space for junk, since the frequency of children’s parties is probably limited or can easily be kept under control. Kids soon want the parents far away anyway; party time is mostly in the warm months. At a certain age, you don’t really want too many teenagers partying in the basement (keyword alcohol, WC use, minor excesses, etc.).
They can go all out with others.... but not in my house, for which I pay a lot of money every month and partly limit myself for half my life. I had that once or twice at our place and consider it a dreamy idea. If 20 parties were actually celebrated over time, one party alone would cause pure building costs of €2,000 - 4,000 per party. For that, I would rather have a foldable garden pavilion, fire pit, wooden benches.....and less bank loan.
There are also 2 more storage rooms right away, while bikes/garden tools aren’t included, so I ask myself WHAT should be there that takes up so much expensive space?
Again, it’s none of my business at all, I just want to say that here—interestingly—you live in completely different worlds, and I can’t even imagine that. I get goosebumps when I see rooms filled to the brim with boxes and junk.

3,000 € per sqm just for the house? Or all in? Just for the house seems to me to be the Lake Constance bonus?

House with foundation slab without kitchen but including floors and painting work. Exterior facilities, garage all extra. In both offers, actually no luxury was demanded. Underfloor heating with air-water heat pump (Weberhaus) or brine-water heat pump (local general contractor). Proper photovoltaic system. Otherwise basically standard. At Weberhaus this means scratched plaster on the walls and woodchip wallpaper on the ceilings, with the local general contractor lime plaster inside. I can only say exactly what is included when the construction description arrives. I guess I will get it tomorrow morning at half past four, the general contractor seems to be an early riser. Then we will also see whether it is the notorious 30 cm or more. Since we have already addressed the topics "slight slope" and "frost-sensitive clay," 30 cm would miss the mark. The same issue applies to the deep drilling, which is listed as included but with how many meters?

.......I would generally ask myself whether I want/can spend tens of thousands of euros on an extra "party room," when I am building a nice, new house with stylish living spaces..... and then for the children too!!! Of course, it's none of my business, but you have to be able to afford it. Whether children, besides having their own room, often their own bathroom, also need their own party room in the house.... hmm. Maybe Papa’s subconscious as a hunter & gatherer comes through and he simply wants maximum space for stuff, as the frequency of children’s parties is probably limited or can be easily kept within limits.

Clarification: I (along with my husband and two minor children) have my house and my cellar, and it is full. The other house with the still empty cellar is a fully basemented semi-detached house, which was originally built for my son and my daughter with their families. Since my son has now moved to his partner (600 km away) due to the long construction time, only my daughter with her family will move in for the time being. The party cellars were thus not intended for children’s parties, but for larger gatherings of friends and family of the two.

Clarification: I (together with my husband and 2 minor children) have my house and my basement, and it is full. The other house with the still empty basement is a fully basemented semi-detached house, which was originally supposed to be built for my son and my daughter along with their families. Since my son has now moved to his partner (600 km away) because of the long construction time, only my daughter and her family will move in for now. The party basement was therefore not intended for children's parties, but for larger gatherings of friends and family for both of them.

You don’t have to clarify anything, I already understand that. Still, the "hunter & gatherer" type of person generally tends to stockpile rooms and things, and the other "type," for example me (non-collector/low buyer/discarder), tends to look more at what I DO NOT need. For example, I also would not pay for a room for adult parties. These ALWAYS take place in the living area, where I like being the most and/or on the terrace. Party basements, whether for young or old, seem outdated to me, something that no longer fits in today’s time. As I said: in MY way of thinking and living. And regarding the frequently mentioned financial budget limits here, I am always surprised now and then WHAT is considered "normal" despite a tight budget, or what one does not want to do without. I would rather spend every euro on great living space. I wouldn’t need such rooms at all and wouldn’t build them now, and we also have children and grandchildren.

The party cellar was therefore not intended for children's parties, but for larger gatherings of friends and family of the two.

Also in my opinion, this no longer fits today's times. Party cellars had their heyday in the 70s-80s (!?), and nowadays I don't know anyone who still uses theirs. On the contrary, I know people who have looked back offended after years/decades that they spent years at friends' houses only "in the cellar" and were never allowed to enter the beautiful living room. We also live in an apartment building with a party cellar, which in 20 years has maybe been used 5 times as such. We quickly repurposed it after moving in.... Anyway, to each their own. And although I appreciate a cellar as such, we decided against it when building the new house. Certainly not least for financial reasons. But this was admittedly because we were not willing (nowadays) to spend excessive money on "junk storage rooms" additionally.

Since I have already seen full-screen screenshots from you several times, allow me to casually recommend a nice little program called the "Snipping Tool," which you already have on your Win10 and should alternatively use for screenshots ;)