slab

It really depends on how it was built in the first place. If it was put in after the building was completed, you would remove it in reverse order.
Base moldings, finished flooring, subfloor and floor joists.
Is this in a basement or a garage?
Ron

Mrtngui said:

The house caught on fire. So when they rebuilt instead of pouring a new slab they built a subfloor with plywood and studs. We would like to do away with the subfloor and add a slab on top of the other slab

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Depending on what surrounds this added structure, an additional slab may be inappropriate.
Just because you have a fire, would not mean you would build the structure you indicate. Why would you cover the thing that wouldn't burn, with something that will burn.
It would help if you told us where this structure was located in the house.
Is this a slab on grade house with no basement?
Ron