At some point the original owner of the house I’m working on decided to convert the garage into a master bedroom. That is a picture of the method he used to avoid having a concrete floor. Those are 16-foot 2-inch by 12-inch slabs of pine. They are not cheap, and they are normally used as joists or support beams. The ‘normal way’ would have been to use treated 1 by 2s and ¾”plywood achieve the current height. I would have raised the height to the same level as the rest of house, so you didn’t need to step down into the room. Of course, I would have also put in a door that was wider than 24 inches so you could move things in and out without pulling out the stove.
This house is really messed up.