Correct construction of garage floor?

Hello everyone! I am planning to convert an old utility building at my house into a garage. The exterior walls and ring foundation will remain old. Only new openings for doors will be made, and the floor needs to be redone. And now it's about the floor. What is the correct structure?

1) From bottom to top:
Cardboard / foil as a water barrier
Concrete slab
Insulation
Floating screed

2) From bottom to top:
Concrete slab
Foil against groundwater
Insulation
Floating screed

3) Completely different variant?

I look forward to a little helpful answer.
And regarding the insulation: what do you recommend? And at what thickness does it still make sense and from when is it just a waste of money? (Garage is to be heated).

Thanks

Which floor is currently installed? What is the heating intended for? (Heating the entire room or only enabling working and tinkering on cold days)

Current floor:
Almost everything and nothing. Different concrete floors, remnants of some foundations. So none of it is usable, it all has to go.

Heating:
Exactly, in the end it should allow comfortable tinkering on the car & motorcycle on cool days. Being able to have a beer during a chat about engines in winter without having to wear a jacket. So if I have it at around 14 or 15 degrees in winter, that is completely sufficient for me. It should not be a living / sleeping area.

Hi

I would think of a completely different setup.

Excavate, a capillary-breaking layer, then XPS also as formwork in the edge area. Then reinforcement and concrete. Troweling it all at the end results in a good and load-bearing garage floor. Whoever wants to and has sufficient insulation installs underfloor heating right away. That is how it is planned now in the garage and also in the hall for my truck.

Olli

Thank you. So the underfloor heating is not necessary, so that’s off the table. And the rest sounds good. That’s actually how I had envisioned it as well. Until I heard that you can’t get the 10 or 15 cm thick concrete layer (i.e. the slab) as smooth as screed concrete. That’s why the screed layer should be on top... How many cm of XPS makes sense?

For me, a low-end solution would be enough. Level the ground a bit if necessary and lay plastic PVC sheets where cars are parked and the workshop area is. When it gets cold: gas burner heating. Naturally, it is better as suggested by Olli.