So, this concerns §648 of the Construction Contract Act. The 10% flat-rate compensation in the event of termination by the client for reasons not attributable to the construction company.
There is a free right of withdrawal with the wording:
The client can terminate the contract for the construction of the house free of charge without giving reasons.
The termination must be sent in writing by registered mail to the company no later than _____.
If the client terminates late, clause 14 of the individual terms or clause 15 applies (there it states the 10% flat rate amount due to lost profit).
Apparently, this is not about §648 of the Construction Contract Act itself, but presumably the cancellation policy of the house provider, which quotes an excerpt from §648 of the Construction Contract Act. The "individual terms" are probably found in their GTC. A "late" termination will accordingly not relate to the expiry of the price binding period of the offer but to that of the withdrawal period. Within the withdrawal period you can
withdraw from the contract; after the expiry of this period, you can only
terminate. The withdrawal is granted to you by law and must not be accompanied by claims for damages. Once the withdrawal period has expired, the contractor can validly agree in their GTC that they are entitled to a flat-rate compensation for their previous expenses (or lost profit). A price binding period in the contractor’s offer is an entirely separate matter to be considered independently.
Strangely enough, it says on every page of the individual description: This price is valid until 22.04.2022.
In the contract terms it says: The total price is guaranteed for 12 months from the signing of the construction contract....
If you now conclude the construction contract after the aforementioned price binding period has expired (and have it confirmed that the originally expired conditions still apply!), then the price is guaranteed for 12 months as of the date of signature. There is nothing strange about this; the first is an offer binding period and the second is a stability guarantee for the prices agreed upon at contract conclusion.
I find this difficult because we still need to make some changes to the house.
In this regard, you should have recognized from the relevant threads that this means "red alert": at this stage, it is clearly still too early to already sign the construction contract. First choose the suitable house model (and preferably also make a preliminary building application for it, and of course a building site survey), any contract conclusion before that would be premature!
You simply have to expect price increases in the meantime and plan the house accordingly smaller, as well as ceremoniously put the Dolby Surround fireplace and the disco lights in the shower on the chopping block. You can also live without having "Colani" on the toilet bowl ;-)