Make a sprite called zone. That will be your "camera zone". Overlay every room with it, separetely. So you clone it (CTRL + drag)
Something like this
Then, use this event. The settings (400 and 256) depend on the size of your layout. Put half and half in each.
Make a layer intended for the zones, it'll make it easier to map and you'll be able to lock them.
I got this from a capx I found around the forums.