How to do a window to wall ratio per room

Hi,

We were planning to calculate the ratio of a certain type of curtain panel to the overall curtain wall per every room in Revit. However, our rooms are in one model called interior and all curtain wall and curtain panels are in another model called SHELLandSTRUCTURE. Now my own script encountered some problems while retrieving elements from linked mode. As shown in the picture below, the result is null. How am I supposed to fix this?

Thanks you so much!!!

Is your Curtain panels inside room?

Actually no. They are on one edge or some edges of the room.