Custom Player Classes

So I'm creating a magic mod and I have different elements to choose from with spells. But I want to make it so only that element can use the spells. The way I have it set up, is I have a book and at the end of it there are 6 buttons to choose your element but I want it so that the player can only choose one. The way to get the spells is to talk to a wizard teacher of that element and by doing that you will be given a spell and your wizard level will increase letting you use that spell, and at the final level you will be able to choose a secondary element to use.