Notary fees. Who should bear them?

You don’t have to define it as rent, you can call it compensation payment or whatever else. Especially at the end of the house construction phase, he won’t want to deal with it anymore. Or he does it as cheaply as possible... I find a fixed amount per started month the most sensible...

Well, I would maybe also forego rental income since you would have to pay taxes on it. The house has a rendered facade that should be cleaned or painted at some point. I would rather make the seller an offer that he takes care of this and may live rent-free for 3 months as far as I’m concerned. I wanted to have the facade cleaned anyway. Or what do you think?

So call these monthly installment payments whatever you want (rent, default payment, penalty fee, or similar).

The point that was getting at is: A means of pressure is contractually fixed with the seller. This means of pressure is then applied so that the seller comes out of his stance "the buyer must show maximum flexibility and accept the postponements – I as the seller can sit back" and adheres to the agreed date, since otherwise he suffers financial losses. Hence also the proposal to stagger the amount of these payments. The longer he delays, the more expensive the monthly installment becomes.