Masking occlusion for roof in camera tracking scene

Hey, everyone! I am trying to do my first animation using motion tracking. I shot some footage of my front door and want to have security cameras come down through the roof (sorry for the horrible description. the picture will probably clear that up). I’m trying to figure out how to set up masking so that I can only see the camera when it comes down through the roof and not before. Can anyone point me in the right direction? I have put the roof geometry on a separate render layer and made it shadeless (not indicated in picture). I forget what I tried after this because I accidently forgot to save haha.

Also, I am having this weird problem where when I hook up the output of a node to the viewer or compositor it does not show up. This is despite the fact that the little picture on the node is correct.

nevermind. got it working

amartin7211 I like the Idea you are doing with this and would be interested to know how you did it. I am sure others will share in that interest so please do tell Please and thanks