How can you make your butt bigger and rounder?

By chance have you tried Pilates or yoga? I heard Pilates or yoga flattens the butt...building muscle is probably the only thing that will help it to get bigger. I have heard about squats and lunges, but I am not exactly sure how many and how often these should be done. Look up exercises to build "glutes". For building up the rear end do squats and lunges