First alleged fixed price and now additional costs - legal?

And what is supposed to be included in the 200k? At that price, I rather suspect that another 100k and not just 10k will be added on top....

That is also my suspicion. What else can I say about it?

Unfortunately, I did not agree to that in writing because he already referred to the written form, "that's already stated there."

You misunderstand that. That has nothing to do with you.

Your question is answered. Everything is completely legal. What is your goal? To get out of the contract?

Try to come to an agreement with the general contractor and get out of the contract. If he insists on the 10%, try to negotiate a lower amount as compensation. In my opinion, what you should definitely not do is build, even if they say it’s only 10-20k€, because that’s not true.

So pay your lesson and move on. I might consider consulting a lawyer, but the likelihood is high that you won’t win, as these are standard contracts.

No matter what, you will have to pay the lesson. You won’t be the first this has happened to. Just google it…

https://www.hausbau-forum.de/threads/chance-ruecktritt-Town & Country-Bauwerkvertrag-andienungsrecht.6986/

I would definitely ask a lawyer. As far as I understand, no money has changed hands yet.

Google it

"Termination of a construction contract possible without 10% contractual penalty?"

A specialist lawyer states that everything is legal, and let's be honest, the original poster is not able to refute that the general contractor did not incur material and personnel costs of this magnitude.

Anyway, the matter is settled. The original poster won't get out of it without compensation, writes the lawyer.