Rooms don't always work well across linked files, so sometimes it is better to copy the actual rooms from a linked file.
The process is to turn Rooms and Room Separation Lines into a Group. Turn the Group into a Linked Revit file. Then Insert the Revit file into the other project file, Bind it and Ungroup.
SET UP A VIEW
Open the Revit project file that has the rooms you want to copy.
Turn off everything in a plan view except Rooms and Room Separation Lines (turn on Room; Interior Fill to see all rooms).
If you will be doing this multiple times either create a View Template to apply or special views with visibility settings as above.
Save your file before proceeding as you do NOT want to save after doing the following instructions.
CREATE THE GROUP
In the drawing area, select Rooms and Room Separation Lines.
Click Modify > Create tab > Create Group.
Give the group a name. Use a name that identifies the group - e.g. Rooms L05
CONVERTING GROUP TO LINKED REVIT MODEL
In the drawing area, select the group.
Click Modify > Model Groups tab > Group panel > Link.
In the Convert to Link dialog, select:
Replace with a new project file:
Creates a new Revit model. When you select this option, the Save Group dialog opens. Navigate to the location where you want to save the file.
If you want the new link to have the same name as the group, leave the default name, otherwise enter a name for the link, and click Save.
If there is a linked Revit model in the project with the same name as the group, a message displays to indicate this. You can do one of the following:
Click Yes to replace the file.
Click No to save the file with a new name. The Save As dialog opens, where you can enter a new name for the linked Revit model.
Click Cancel to cancel the conversion.
4. CLOSE > DO NOT SAVE PROJECT.
CONVERTING LINKED REVIT MODEL TO GROUPS
Open the Revit project file that you want to copy rooms to.
Go to a plan view of the correct level.
Insert tab > Revit Link. Use Automatic - Origin to Origin
Select the linked Revit model you just inserted.
Modify tab > Revit Links > Link panel > Bind.
In the Bind Link Options dialog, select the elements and datum to include in the group, and click OK.
If there is a group in the project with the same name as the linked Revit model, a message displays to indicate this. You can do one of the following:
Click Yes to replace the group.
Click No to save the group with a new name. Another message displays indicating that all instances of the linked model will be deleted from the project, but the linked model file will still be loaded in the project. You can remove the linked file from the project by clicking Remove Link in the message dialog, or you can remove it at a later time from the Manage Links dialog.
Click Cancel to cancel the conversion.
6. Select the Group, Modify tab > Model Groups > Group panel > Ungroup.