I often dream of returning to my childhood home. There are extra rooms for me as well. The dreams stick with me for some reason, more so than other dreams.
I also have a dream about my current home where there is an extra set of rooms, unused like the rest of the family never go there.
It's so amazing that you have these dreams as well, I wasn't aware that my dream is not unusual perhaps because I don't usually talk about it. I never dream about my current home in which I've lived for 17 years now.
Actually your dream was an eye opener for me as well. I use to dabble in dream interpretation, but never ran across that one. And the little extra link in the comments was pretty neat. Lots to think about for sure