You have a few options.
Building a subfloor on uneven concrete.
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As a result the material for the subfloor will acclimate to the temperature and moisture content of the room expanding or contracting before the installation rather than after.
Grind the floor use a self leveling compound or use a subfloor to get it pretty close to even as possible.
Alternate subfloor system use a minimum 3 4 inch cd exposure 1 plywood sheathing 4 foot by 8 foot sheets.
Place 16 inch planks perpendicular or diagonal to direction of flooring.
Begin by cutting sheets to 16 inches by 8 feet or smaller panels marked 3 8 of an inch deep on back and a minimum of every 12 inches across in width.
The result is a subfloor that protects finished flooring from cold and damp concrete based floors.
It is best to lay the flooring plastic side down directly onto the cement floor.
There are many reasons that a floor surface or subflooring can be uneven.
In a perfect world all the old flooring and subflooring would be removed and have everything leveled with a brand new subflooring surface.
One of the simplest options is a sleeper based subfloor.
The most common reasons are either a basement or other concrete based surfaces or a remodel that has various levels of subflooring.
Fixing an uneven floor is just more than leveling.
A good carpenter will install sleepers using shims and once the sleepers are in place and leveled you can install the plywood overtop.
I have listed a couple of forgiving flooring materials carpet and vinyl to use over uneven concrete floors.