Okay, here are two photos of the project, after I have (desperately) tried to integrate the ceiling beams with the ground floor. To no avail, as you see. From the interior, they are still not visible, the check-box remains checked, I cannot deactivate the ceiling:

Photo of the exterior (854K):
http://pix.toile-libre.org/?img=1421750647.png

Photo of the interior (522K):
http://pix.toile-libre.org/?img=1421750329.png