Hi,
the use of Metaspace depends on the number of classes that an Extension uses, so it's not necessarily tied to the number of Rooms you create.
Normally you can run thousands of Rooms with their Extensions and not worry about metaspace that much.
The first suggestion is to make sure that you are not packing your Extension's dependencies with your Extension. In other words if your Extension code depends on many external jars, make sure these jars do not get packed into the final Extension jar.
This is to avoid that dependencies end up in the same class loader as the Extension and create lots of extra metaspace, instead those dependencies should be deployed under SFS2X/extensions/__lib__/ which is loaded by the global class loader.
For more info on Extension class loading check the documentation here:
http://docs2x.smartfoxserver.com/Extens ... assLoading
Cheers