Since users can choose to go about this in different ways, it would make more sense to me if a more generic term was used in place of "Room" to represent a drawing.  To click "Add New Room" or "Open Room" doesn't make that much sense if the drawing does not in fact represent an actual "Room".  In the job tree, the term "Category" (for the folders) is generic, allowing it to be used to represent a variety of things without confusion or conflict.  However, the term "Room" is very specific, and since not everyone actually follows the "drawing=room" concept, can be confusing or require training to understand.  If it simply said "Drawing" (or similar generic term) it would apply to a much more broad collection of job tree setups.  Also, if that were the case, "Room Properties" would switch to "Drawing Properties" (or similar), since they apply to everything inside of that drawing.