The key thing to understand here is that revit rooms exist only in one phase.
Revit room tag.
Room tags can display values for related parameters such as room number room name computed area and volume.
Revit displays a warning if the room is not in a properly enclosed region.
As an alternative use the tag all not tagged tool to tag all untagged rooms in a view.
Found this very useful.
How to create room tag including width x depth parameters and a nice use of maths room length.
So you can copy room areas.
Rooms and room tags are separate but related revit components.
To tag a room open a plan or section.
When you create a room if it is properly bounded by elements such as walls and room separation lines revit computes the room area between the boundaries.
Rooms are model elements in revit like walls and doors.
Fortunately whenever you copy an element in revit it will always take on the phase of the active view regardless of what it was set to before.
This tool can be useful for example when you place and tag rooms in a floor plan view and you want to see tags for the same rooms in a reflected ceiling plan rcp view.
So you need a whole new set of the applicable rooms for each phase.
Perimeter 2 sqrt perimeter 2 2 4 area 2 room width.
As described in the article how to define room bounding elements in revit many element types are room bounding by default such as walls floors ceilings etc.
Area room length example included.
If you do not use the tag on placement option when creating rooms you can tag rooms later.
In revit you need to show room areas in different phases and are not sure how.