Thickness of concrete slab for 2-storey building

Alternative would only be to put something thin down for parking space for cars/office containers and remove it again later.

No, then rather replace 1.5m of soil and have a compacted fine grading created. It is needed anyway and will be sufficient for the other foundations later in 80% of all cases.

Nothing is supposed to be built at first, but only the foundation slab for the next 2 years....

Not allowed!

demolish

It is spelled demolish!

The project is overall extremely odd. What is behind it? Why is a slab of unknown thickness, height, and dimensions supposed to be placed there for two years now?

As already mentioned, a slab without a building permit is out of the question. Surveyors, structural engineers, everyone has to be involved. And then you want to add a few centimeters plus steel... you are talking about four-figure surcharges, do you realize that?

I think this is about the "stroke of genius" *LOL*, a court sealing for the purpose of creating a level surface for temporary structures to be used later as the foundation slab for the eventual building. The responsible branch office of the Patent Office is located in Schilda ;-)

Nothing is supposed to be built at first, only the floor slab for the next 2 years

Unusual approach. Why do you want to do that already now?