... When we build, we want to do it only once and then do it right (with everything included). Nevertheless, of course we don't want to take on too much...
Well, McEgg, one should also consider what and how much one really needs. What does "then do it right" mean? Most of the time, people possibly live in cramped conditions and suddenly fall into a size frenzy. For how many people does one want to build? If you are five, in 20 years the rooms are usually too few, the basement is only used to store things you don't really need anymore, the steam shower and whirlpool are not used because the effort of cleaning is too great. A double garage is a luxury, one car can also stand under the carport, and so on and so forth. A small family curses the long routes. Therefore, it is worth thinking about your real priorities and daily routines; afterwards, you can cut out several square meters and unnecessary costs. Usually, a 10 sqm bathroom suffices instead of the bathroom hall ;) When it comes to small luxury, it should be said that this is not yet reflected in the calculation.
Personally, I also believe that building "only once" is not the solution. Usually, in 20/30 years you have completely different needs that the built house no longer covers, so it makes sense to consider changing to a "new" property.