You position the floor chipboard with an expansion joint against the standing wall stud, then you erect the interior walls on the floor chipboard. That's how I would have done it anyway.
The door frame is placed in the wall studs but stands on the interior floor, so if you're going to lay parquet, do it before installing the door frame. The parquet can have a seam under the threshold if necessary to conceal it, and you won't need to deal with trim strips, etc.