I taught my dog to give high fives by holding my hands up above her head and holding her favorite treat in one of my hands. Once she stands and puts her hands on mine, she gets the treat.

Roll over was tougher. Once your dog learns to sit and lay down, you could use it to your advantage. Have her lay down then move the treat over to the left or right (my dog only goes to the right) and give her a small shrug to make her roll over. After much practice, she'll get it.