First alleged fixed price and now additional costs - legal?

No, that is not true. That is not mandatory.

true, that is not mandatory. But if the employee does not make use of the opportunity, he has no chance later to make an addendum due to local conditions. Then he is out of luck.

That's true, it is not mandatory. But if the contractor does not make use of the opportunity, he has no possibility to submit a supplementary claim later due to local conditions.
Then he's out of luck.

Depends on the contract. It has already been discussed two pages earlier.

And the usual remaining €50,000 additional construction costs, have you planned for those? Do you have the clause about the failed financing in the contract?

I have planned €16,000. The plot is already there. €10,000 for development. €1,000 for construction water and electricity. €5,000 for surveyor and other fees. I do not come anywhere near €50,000.

Since you have no financing, you want to get out of the contract. That will incur costs. Reject all additional costs; in my opinion, that will at least provoke a standstill.

Actually, I want to build a house. Whether the franchise system with the incalculable costs will work out, I don't know. Now that I know that they have set up a bottomless pit for me, I naturally prefer to get out. Thanks. I will do that.

As already said, termination is the last resort as a client. What the lawyer suggested is a good idea.

Which services have already been rendered? According to the payment schedule?

Your question has been answered. Everything is completely legal.

What is your goal?

To get out of the contract?

That depends on the price. If I could get out without loss, yes. If the price to exit is too high, continuing construction might be an option, but depending on what the general contractor still has planned for me, that could mean my ruin.