Twins for the kids

I have 4 children & at the moment 2 have their very own rooms, with queen size beds & two are sharing, but when we build everyone will be fortunate enough to have their own space. As anyone with kids knows, as they get older they love to have friends for sleep overs. How do you set up for the sleep over, do you have a roll out bed under your child's bed, a blow up mattress that tucks away in the