Risotto is a type of dish that is best served fresh, right after cooking. Rice soaks up the liquid as it sits, so that's why it needs to be reheated with additional liquid. While you can make it ahead of time, I recommend that you save or make a little extra stock mixture and store it separately. When reheating risotto, do it in the pan with the additional stock mixture. As far as freezing, risotto does not freeze well so I don't recommend freezing it.