Can a shadow catcher object also be a collision object?

Hi,

This is my first Blender scene. I’ve successfully tracked footage from an eight story parking lot and used the camera setup.

I wanted to drop particle driven balls on the building roofs, but found I couldn’t get the roofs to be shadow objects with collision working. Do I have to duplicate the roofs to a different layer, make them collision, and hide them from the camera, or are there other methods?

Can’t attach or I would include a pic.

thanks for your response.