Haven't met anyone which such a contract. It's usually a fixed value. The owner may choose to raise it every now and then, but laws limit it to a certain amount

Haven't met anyone which such a contract. It's usually a fixed value. The owner may choose to raise it every now and then, but laws limit it to a certain amount per year and there needs to be a reason, for example modernization or other buildings in the area are becoming more expensive. You can of course make a contract that allows for automatic raises, but that is also limited (earliest 12 month after the begin of the lease, only a fixed/absolute value and not percentage) and you can no longer raise the price for the other reasons. There are probably other models, but I don't know much about them.