Your basement floor slopes because of the drain that handles runoff from your furnace, spills, flash flooding, etc. If there is another drain in the basement to handle this, then you can flatten the floors in the livable space with a floor leveler.

Floor leveling compound is for relatively smaller areas such as 4 x 5 feet or less. If this is a floor drain slope then I suggest pouring a floor leveling slurry to flatten the floor. It is like a water concrete that is “self leveling” or “semi-self-leveling”. It can be purchased at wholesale flooring suppliers and is not easily acquired outside the professional community of suppliers.

The volume of fill leveler is substantial when you really calculate the volume required. A raised wood cavity will potentially hold moisture, be un-vented and promote stagnant air. This below floor cavity in the basement will potentially encourage mold growth and maybe a not so healthy environment.