Here’s a quick way to lock your ceiling grid in place so it doesn’t move in your model. When you have placed in your ceiling grid Revit allows you move the setting out by selecting it and dragging it, but if you don’t wish for the ceiling to move then you could always pin it in its location.
1. You need to select the ceiling boundary so you can lock it. To do this move your cursor to the ceiling boundary edge, using the TAB key to cycle through the selection until you see the ceiling boundary heighted. Now select with your cursor.
2. Click Modify|Ceilings tab > Modify > Pin. This will now locked the ceiling in place.
If you need to unlock the ceiling select the ceiling and unpin either from the ribbon or on screen a pin will show in the middle of the ceiling.
You can move walls and the ceiling with still adjust accordingly but you won’t be able to rotate the ceiling grid.