Single-family house assessment 170m² - construction cost overview underestimated?

Are no brands specifically mentioned in the offer and is the material from Romania or similar? A friend is building a house that way and is operating in a similar range... Outdoor facilities, especially on a slope, are an absolute joke, just barely enough to plant a hedge around the property. Terrace slabs alone cost almost as much with us, without labor costs, substructure, etc.

So a colleague built a detached house in Pforzheim BaWü in 2015, also on a slope. 160 sqm without garage, standard equipment. He paid about 350k including incidental construction costs. Afterwards, however, a few thousand more were added for the outdoor facilities. In the end, it was definitely well under 400k.

In NRW you will probably get away a bit cheaper, since the labor costs here in the South are simply higher.

With or without a basement?

Are no brands specifically mentioned in the offer and is the material from Romania or something like that?
An acquaintance is building a house that way and is operating in a similar range...
Outdoor facilities, especially on a slope, are an absolute joke, it’s barely enough to plant a hedge around the property.
The tiles for the terrace alone cost almost as much here, without labor costs, substructure, etc.

Brands are not specified.

Thank you for your assessment

Brands are not fixed.

Thank you for your assessment

But that is not insignificant, are the windows with Schüco profiles or from Pax etc. or imported from Poland.
Door panels are also available in the hardware store for 29.90 or for several hundred euros. The same goes for tiles or laminate, 20 euro tiles or 50 euro.
Which heating exactly, which ventilation, scope of electrical installation and not standard or upscale as a specification but actual number of network, TV, sockets, etc.
Just as a rough estimate, we did a lot ourselves and paid about 240,000 for 135m² plus basement (partly in living space quality), excluding land, furnishing, additional costs and outdoor facilities.
Own contribution can be estimated at about 20,000, but this was signed 5 years ago. So, due to KfW and inflation, you can certainly calculate another 15-20% on that today.

Just as a rough estimate, we did a lot ourselves and paid about 240,000 for 135m² plus basement (partly to residential standards), excluding land, furnishings, incidental costs, and outdoor facilities.
You can estimate about 20,000 for own work, but the whole thing was signed 5 years ago. So with KfW and inflation, you can certainly add another 15-20% on that today.

We have the same size, and +/- 80k more (construction started this year).

Sounds very little. I would study the construction service description very carefully here. Are there reference houses? Other builders of the provider?