Um....I think Millsberry is kinda about getting and spending...having a nice fantasy house and clothes and such....one assumes one's house is more desirable with a bathroom than without.
I venture this opinion based only on some of the Millsberry questions I have seen....and I think I looked it up at some point for some reason.
Trinniboy...here are answers given on other fora to your question:
You go to the construction store and there's a button called Add A New Room , click on it and you can choose where you want it and what room it's going to be and what you want to call it.
Check out my Millsberry Account : alicia_is_th3_b3st