Call, ask, obtain alternative offers. You have to do that anyway.
You are welcome to post an anonymized offer here, then we can help more specifically.
Hi, yes, if I were building turnkey.... I contract all trades myself, know craftsmen for each trade, and have already built two houses myself with a lot of own work. However, that was already 10 years ago........ I am calculating total construction costs of 400,000 €, the region is rural and the construction site is very easily accessible. Still, thanks for your assessment. Regards Markus
That doesn't help you at all, except for own work. It essentially also depends on the equipment.