I am not sure if this is the "technical" way to do it but what I did to avoid going gallery all the time was placed the rooms I wanted to keep on an empty lot and clicked up top on the little folder and hit save to library. This made the room visible in both my gallery and when clicking on the saved rooms option at the bottom of the screen while in build modes "styled rooms" option.
I was going to post pictures but it wouldn't work, so hopefully that makes sense.