Walls, floors, and ceilings can have different materials from each other by changing their details
But the individual floor material can’t be different from other floors, if that’s what you mean, because they are an instanced mesh. If they need to be, I would make them empty and add it manually. Or use a 2nd SquareBuilder if it’s a whole area. It’s good for making the bones of an area, and then details are often more practical to do manually.
But if Material Override is set, it will override everything.
Decorations: just specify the Floor.Square (ex. 1.4, 1.5) and pick a mesh or actor. (I seem to be using an outdated version that’s missing options 
) More details on decorations here.
Floor.Square you can find like this
