initial brainstorming

Starts at €400,000... you can say that much :)
A good friend of mine is soon building exactly as you describe (you know you have quite a bit of expensive luxury in there... KNX?) 145 sqm WITHOUT a basement and no exterior landscaping included yet, cost breakdown from provider 1 and 2 at €430,000 each... as I said, without a basement.

Well, I find €400,000 a bit exaggerated now.
We are building with 240 sqm and also have all that he lists above (except the integrated radio and the home automation) and are WAY below that. Ok - we don't have a basement - but if I then deduct the 100 sqm more living space, the converted attic, and the very expensive earthworks (soil replacement), he can easily have the desired basement for that amount.

Why do you need so many network connections???? :eek:

No idea, ask my husband. :-) I also find them unnecessary. I always compare it to an earlier house build where they put a telephone line in EVERY room so you could connect phone and internet. Today (15 years later) no one needs that anymore. And I would almost claim that when the kids are old enough that this might be relevant, it’s already obsolete again, because TV is watched via laptop and internet and internet runs over WiFi. But everyone to their own taste. As I said, we also have it in every room.

You want to fit 4 bedrooms + bathroom + corridor + stairs on 145 sqm upper floor total area? That could get very tight. I don’t know if your wishes aren’t too much there.
If you want to build the basement anyway — maybe the office in a heated basement room with a large light well?

Well, if he makes all rooms only 12 sqm in size, that will work. However, I wonder how usable a 12 sqm bedroom is. A 4x3 meter space just fits a bed, but there is no space left for a wardrobe - especially since a door and a window also have to go somewhere.
Otherwise, the study could also alternatively be accommodated on the ground floor. There he also has some room to spare.

: are the 145 sqm distributed over ground floor and upper floor or does that include the basement?

Without a basement, as I see it. I don't find 12 sqm small. We still live in our apartment and Junior has such a room with a large wardrobe, 2 dressers, a bed inside, and in the middle there is a nice rug to play on. In our house, the children's rooms are 14 sqm, anything more is nonsense in our view (but I must admit that our children will one day get their own living room in the basement!)

I find it more important to lay empty conduits for new technological advances like fiber optic cables. Network sockets have become unnecessary if you don't want children to be bombarded with media.

...from the cost side I agree with Bautraum2015. From 400 thousand € without the land, including development, double garage, outdoor facilities and kitchen. I am not an expert and once calculated our house (2011). It is somewhat smaller, also has geothermal heating and controlled residential ventilation, but not the technical gimmicks (WLAN and powerline are enough for me) and no fireplace... Wastl is right - the study on the upper floor should not come at the expense of the size of the children's rooms. And an office can well be in the basement - with a nice light courtyard in front of the window - or you find a hillside plot - here you also get nice light into the basement.

Haha, . I actually meant G-Star when I asked about the square meters :)

Without a basement, as I mean. I don’t find 12sqm small. We still live in our apartment and Junior has such a room with a big wardrobe, 2 dressers, a bed in it, and in the middle is a nice rug to play on. In our house, the children's rooms will be 14sqm; more than that is nonsense from our perspective (but I have to admit that our kids will once get their own living room in the basement!)

Yes, the children’s rooms work. I do think a children’s room should be at least about 14m2 (depending on the sloping roof), but that they work and also have enough space to play is unquestionable. (ours are 16m2, almost square, hardly any sloping roof, and the kids also have another room as a play and living room :-) ) But a 12m2 bedroom without a dressing area is really, really tight. Around the bed, there are just narrow walking paths of 50-70cm, depending on how the bed is placed. Comfortable is another thing.

Of course, it depends on the age. The older, the better is one or the other extra square meter. We are now planning 14-15 sqm, almost rectangular, full floor, and each with one floor-to-ceiling window and two casement windows (with light you can also suggest size). Back to the topic: 400k is in my opinion the minimum at the current construction prices. Trend increasing over the years.

so the 145m² are intended without the basement.

You are right about the study, maybe it would be better to put it in the basement after all. Although the room is also supposed to be for our pet. Hmm well, that has to be done based on the plot and the floor plan.

The many network sockets (although I think that is still too few) are needed for so many things. There is already enough radiation everywhere, so you want to avoid WLAN as much as possible. And who would like to transfer data at 300 Mbit when they can also transmit it via cable at 1000 Mbit ;-) In addition, movies etc. run more smoothly via cable. Just in the future living room alone, I need 3 network connections or a switch due to the AVR, multimedia receiver, and TV.

I also estimated the costs at around €400,000, nice that you roughly agree with me there ;-)