Property acquisition tax on land and also on construction costs?

I can only agree with that. Two different contracts with two different contracting parties, private or not. This now absolutely says nothing beyond whether in the end it becomes/was a tied deal or not.

Problem _could_ be that the house was signed beforehand. It is better to first sign the land, and then independently the house (contract for work, not a purchase contract). But let's wait.

I think everyone gets the form.

Can a developer build a building without land? I think there is still a fundamental misunderstanding here, as already mentioned. The construction partner is probably more likely to be a general contractor (GU) or main contractor (GÜ).

The timing of the contract conclusion is initially completely irrelevant to the tax office. They are only interested in the extent to which there is a connection/dependency/coupling between the land and the building. This needs to be clarified/proven. If it really were a developer, in my opinion, the land and the building would definitely be linked and therefore the real estate transfer tax would have to be paid on everything.