Is filling the entire plot necessary? Cost explosion?

I believe there are partly regulations in the development plan about how far you may go above/below the future street level with the height of the house? Or am I totally mistaken? I believe even if you had to fill up 40cm, it probably wouldn't become a financial bottomless pit.

I think there are sometimes regulations in the development plan about how far one is allowed to go above/below the final road level with the height of the house? Or am I misunderstanding that? I think even if you had to fill up 40cm, it probably wouldn’t become a bottomless financial pit.

These usually apply to the finished floor level of the ground floor and often lie in the range of 50cm above the middle of the street (manhole cover finished road). Filling is cheap, removing (landfill) is expensive.

Unless you want to seal everything later anyway, you have to apply 20-30cm of topsoil one way or another. Here, almost everyone has piled up 150m³+.

As previous speakers have already written, you don’t need to panic about the possible necessity of filling in. Depending on the type of house and the development plan, it can even be an advantage for you! The expensive part of earthworks and preparation is rather the disposal, so in this case you could even benefit from the lower actual level. Even if you theoretically had to fill in the entire property, it would only cost you a few thousand euros (depending on the material). However, it should be taken into account that with cellars or foundations there will be excavated soil anyway, which can be "distributed." After all, perhaps some neighbor will be happy to dump their excavated soil (provided it is "clean") on your property. But either way, I would see the situation more positively than negatively and definitely build above street level.