Calculation of strip foundation for a bungalow

No, what he means is that you have to remove/excavate far more than 20cm. Calculate with 1m. At the same time, you can't use all the excavated soil everywhere for piling/filling because you need load-bearing material for that. That means in the end you have 400 cubic meters lying around on the property, of which you can use, if you're lucky, 100-200 cubic meters. So plan on having to dispose of 200-300 cubic meters -> expensive, if the soil isn't absolutely great, even more expensive.

I mean that you have to fill up significantly so that a 20x20 area is reasonably level and the house does not end up tilted. Accordingly, the groundworker will then hand you an invoice for additional work and gravel.

Of course, you can also model a dike around the garden, but it is usually not allowed...

Hügelbeete is the magic word for it

I hope you have a construction companion/site manager on your side who supports you.

Get several quotes, then you'll know if the price is right. But for that, you (!) have to specify the scope of services so that it is comparable.
If you can't do it, pay someone to do it.

Separating drainage and foundations is such a typical interface error... This needs to be coordinated regarding the heights, etc., and where which pipes are needed in the foundation area.

Ok but now to the core of my question can someone estimate the price for the strip foundation?