I have made a new variant - just ceiling mod.
Since this ceiling-patch is hidden under the floor, here is my tip of building:

1. Find "Artrui Movable Ceiling 2x2" under Build mode/Pool/Pool accessories.


2. The patches will be placed one floor above the room. Let the grid-marks in build mode visible and place the ceiling-patches in grid from behind to front, from right to left and put all of them in the same direktion. During this placement, while you are holding a ceiling-patch, you can see it's green footprint.


3. Once you've placed this ceiling patch, it goes disappear. But you can still edit the placed patch. Point there with your mouse, the cursor will become a little hand. Click right there. You will see: the ceiling-patch is seleted again.


4. After all the ceiling-patches are placed. You could remove the whole ceiling of the room to prove whether all the patches are placed in right position or not. Click the wall of the room to select this room.
(I've tried to build it in an other order: remove the room ceiling at first; enable MMO cheat; place the patches; close the ceiling. Some patches are slightly higher than the others. Thus, I advise you place the patches on the closed floor/ceiling at first.)


5. Move cursor onto the yellow highlighted line. It pops up a small frame with text "remove ceiling". Move the cursor onto that text and click. The whole ceiling is removed.


6. Now, you can see the placed ceiling-patches. In this example, the at last placed patch is not in the right position. Ignore some transparent issues of these patches. They will have fine looks if the ceiling of room is covered again.


7. Just fix the position of that patch. Click the wall again to select the room. Move cursor onto the yellow line, then, move onto the text "build ceiling", click.


8. Move camera into that room in play mode (#1, step8-12) to see the effect of this mod ceiling. Enjoy!