Use the following procedure to make the host project recognize the Room Bounding parameter of elements in the linked model.
To use room boundaries in a linked model
The status bar displays the following:
RVT Links: Linked Revit Model: <model name>.
Now you can place rooms in the plan view, using the boundaries defined by room-bounding elements in the host project and the room-bounding elements in the linked model. See Creating a Room.