You can copy rooms from one phase to the next to preserve their properties.
Rooms in Revit let you specify properties for a region of the building model, such as a Name, Surface Finishes, and Level Offset. After setting these properties to identify the characteristics of a room in one phase, you may want to use that room specification in another phase. This is useful when changing an existing region with new construction. To do this, copy the room from a view assigned to one phase to a view assigned to a different phase to preserve the properties.
For example, to copy room specifications from the Existing phase to the New Construction phase, use the following procedure.
To copy room specifications from one phase to another
The room is added to the New Construction phase with the same properties that were specified in New phase.