This is my personal Ragnaros Build.

[Level 1] Shifting Meteor is a talent Quest that once completed will allow you to redirect Living Meteor once while it is active.

[Level 4] Fire Ward is a talent that causes Living Meteor to grant you a spell shield reducing the damage the next ability that hits you. It holds up to two charges.

[Level 7] Molten Power is a talent that causes your next Living Meteor to do increased damage based on how many Heroes you hit with the previous Living Meteor.

[Level 10] Lava Wave is a talent that fires a wave of lava up an entire lane, instantly killing minions and moderately damaging Heroes caught in the path of its' devastation.

[Level 13] Resilient Flame is a talent that activates whenever Ragnaros is stunned for at least 3 seconds, reducing damage by half.

[Level 16] Meteor Bomb is a talent that causes Living Meteor to explode at the end of its' path.

[Level 20] Lava Surge is a talent that allows you to fire up to two Lava Waves at the same time.