Construction on someone else's property with subsequent purchase

Basically, we would also add the difference on top, but so far our acquaintance has been uncooperative in this regard.

Then you can already expect that she will be uncooperative with many other things as well. How determined will she be to straighten things out? Would it be an option to wait 5 years with the construction? I would keep the property in mind, but mentally check it off and simultaneously look for a new one.

You mean the heritable building right ;).

Of course :D

So with us, the repayment must also be fully completed before the expiration of the heritable building right; ideally, the additional 10 years would also be desirable for us at least. But in the small loan sector, it's often pushed through by the market even without the additional 10 years. However, the appraisers naturally proceed according to regulations when determining the mortgage lending value – and then it's definitely not suitable for the cover pool.

Due to the circumstances, I can only advise against such confusion. People change, things do as well.
In our case, it was somewhat different, but on the one hand, it was also about the speculation tax, especially about an until then unknown problem with the right of way. A previously responsible notary had meanwhile passed away, the municipality shrugged their shoulders, and we, as well as another older couple, were caught in the middle. Result.
The owner then offered us to postpone it by 5 years, and we had various options examined. The whole thing ended unpleasantly for us and the other family.

Your situation may be different, but it is still hard to understand why the lady does not want to sell the property NOW if she does not have to pay any taxes (she doesn’t have to pay them). She may not even have bad intentions, but it is still strange, and strange people come up with even stranger ideas (just experienced).
The other couple had also questioned the topic of lease purchase, but the problem there was apparently that the tax office would consider the decision date of the lease purchase later than the actual purchase date. Surely thousands of people have already tried to avoid this tax; I would be surprised if it were that simple.
You may feel differently... I am immune to such things. There is no reasonable ground here why she should sell today; she gets the money immediately and pays no taxes on it...
I think you would also have a queasy feeling for 5 years until the thing is through. With such complex matters, something can always happen that even the most experienced professional did not expect. In our case, it was the deceased notary...
You are not yet ready to pay a currently high price for properties, which I understand. But to get involved in such a thing for that... no, I’d rather pay more elsewhere.

Alternatively, the house was not inhabited and also not rented out, right? Owner-occupancy applies, for example, also to weekend or holiday homes that are "used" by the owner themselves. As soon as the garden was "owner-used" for relaxation, it is probably not necessary that the house itself was also inhabited.

That sounds good, the original poster should definitely keep pursuing this. Overall, it sounds as if she does not really want to sell. Maybe she does not want to upset you too harshly? Who originally had the idea to sell the plot of land?

You are not willing to pay a currently high price for land, which I understand. But then to enter into such a thing.....no, I'd rather pay more somewhere else.

Yep. Although land prices at 80€ per sqm are a bargain compared to most home builders in the country. At these prices – usually totally off in the countryside – there is a relatively good chance in most regions to get land. In metropolitan areas, where we are talking about 300-400€ per sqm or in big cities from 1,000€/sqm, I would stay on the case. Here: Offer to buy now or the "acquaintance" can go jump, as we say around here.

Where the land prices of €80 per square meter are a bargain compared to most homeowners in the country. At these prices – usually located completely off the beaten path in rural areas – there is a relatively good chance in most regions to acquire land.

That brings me to a question that has not been answered so far. Where do the €80/sqm come from? Standard land value or just an estimate?