Select the building model by left-clicking on any part of it.
In the Floor Plan View select the linked Architectural model. Make sure that the Select Links tab at the bottom right corner of your Revit window does not have a Red X, or you will not be able to select the model.
Navigate to the Properties Browser and click the Edit Type button. Under the Constraints heading, check the box next to Room Bounding. Click OK to close the properties dialog boxes.