So I made a custom map for my friend to play and when I tried it the FPS couldn't go higher than 11. Does it have anything to do with the amount of rooms or what is the problem that makes Containment Breach lag so badly. I tried other maps but they didn't lag at all.

If you have a large number of rooms that could be the issue. On average facility size is about 80-100ish rooms. I believe going far above that may cause a problem. I dont want to say for sure but there could be some issue causing frame-rate drop too.