I'm not exactly sure how it was done but they created storage closets on unfinished spaces either side of the play room and off of one the bedrooms. (domesticimperfection.com)
We have 1000 sq. feet of unfinished space on our third floor and the only thing standing in the way of doing it..... (theinspiredroom.net)
Our basement has one large family room that's finished, and then has a ton of unfinished space. (mysahomestyling.com)