When designing houses, I add walls usually 10 cm lower than the room's ground level, matching their real physical position, and with solid operations remove them from the multilayered slab. This matches the real construction fast and easily, looks OK on the sections.
When I add a door into the wall, I match it to ground level (meaning a 10 cm high wall is under it). It' OK from all but one viewpoints: this way the wall opening isn't added to the room area. When I move the door down to the wall base, things work (except that the door is 10 cm down in the slab), so other settings must be good.
Is there any chance to have a correct room area calculation? I've checked door/wall/area settings and haven't find a clue.