This requires wooden blocks. They need to be fixed with plugs and screws.
But first, you need to make marks on the wall, with using the water level.After marking, fasten the first block.And on the other part of the wall, fasten a second block.Further, stretch the thread on the beam.And follow the level of the thread , fasten the other wooden blocks .
Then you can put a floor. First board sew screw, then put on a second board. And so all boards.
And in the end sewn plinth to the floor with screws.
That's all the work.