Ways to fulfill the building obligation/building deadline in order to build later

... I've already crossed off a tiny house for myself. In the end, a lot of glued plastic waste remains for, as mentioned above, a lot of money. Too little sustainable for a temporary solution.

Well, that doesn't quite fit. A tiny house, if built "ecologically," is mostly made from sustainable building materials like wood, wood fiber insulation boards, metal sheets, etc.

Much, much less CO2 than concrete/cement or PU and whatever other "dirt" comes from oil

That is why the question was asked how long the building obligation applied ... for us it is 5 years and I would say that anyone who does not manage that never had an urgent need and should not get such a plot ... With 2 years I think it looks different, then you would have to start immediately after purchase with everything so that you can manage it