ᐅ Proper Construction of a Garage Floor?

Hello everyone!
I am planning to convert an old utility building next to my house into a garage. The exterior walls and the ring foundation will remain as they are. Only new openings for garage doors will be made, and the floor needs to be redone.
And that’s exactly what I need advice on: the correct floor construction.

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

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

3) Or a completely different approach?

I would appreciate a short, helpful answer.
Also, regarding insulation: what do you recommend? What thickness makes sense, and at what point is it just a waste of money? (The garage will be heated).

Thank you!

Which type of flooring is currently installed?
What is the heating system supposed to be used for? (Heating the entire room or just making it comfortable for working and screwing on cold days)

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

Heating:
Exactly, the goal is to allow comfortable tinkering on cars and motorcycles on chilly days. To be able to have a beer during a petrol-fueled conversation in winter without needing to wear a jacket. So if I can maintain around 14 or 15°C (57 or 59°F) in winter, that is completely sufficient for me. It won’t be used as a living or sleeping area.

Hello

I would suggest a completely different design.

Excavate, then add a capillary-breaking layer, followed by XPS insulation also used as formwork around the edges. Then reinforcement and concrete. Finally, screed the entire surface to create a solid and load-bearing garage floor.
Those who want and have sufficient insulation can install underfloor heating at the same time.
This is how it is currently planned for my garage and the workshop for my truck.

Olli

Thank you.
So, the underfloor heating isn't necessary, so that’s off the table.
The rest sounds good. That’s actually how I had originally thought about it too, until I heard that it’s difficult to get the 10 or 15 cm (4 or 6 inches) thick concrete layer (the slab) as smooth as screed concrete. That’s why the screed layer is supposed to go on top...

How many centimeters of XPS insulation makes sense?

A low-end solution would be enough for me. Level the floor a bit if necessary and lay PVC plastic panels where the cars are parked and in the workshop area. For cold weather: gas burner heating.
Of course, the solution suggested by Olli is better.