Passive: Chosen of the Storm
As i mentioned before, Chosen of the Storm gives you great dueling potential. However, don't rely on it too much as it's easily shutdown by ignite. Chosen of the Storm will renegerate 30% of your MAXIMUM health. That's the first reason why Volibear is really good with additional health.
Q: Rolling Thunder
Initiation and best ganking spell. Grants you 45% movement speed boost while running towards an enemy. Rolling Thunder gives you a movement speed boost even though you are not running towards an enemy, but only 15%. This can still be used to move around camps faster. I normally max it last because the movement speed doesn't increase with higher ranks.
your most IMPORTANT skill. It deals damage based on your bonus health and based on your targets missing health. This is the second reason why Volibear is so good with health. You will become tanky and still be a damage threat.
E: Majestic Roar
Try using Majestic Roar in a group of enemies because of the aoe slow, its an excellent spell for protecting your carry or chasing down enemies. Remember, Majestic Roar works on Tibbers, Zyra plants, Shaco boxes, Heimerdinger turrets and Malzahar pets.
R: Thunder Claws
This is the reason why Volibear builds Attack Speed and not Attack Damage. More AS means more procs off your ulti, which means tons of damage.
Tip: If the enemy is escaping and there are minions nearby, Thunder Claws will send lightning through the minions, and if the enemy is within range they can get struck by the lightning as well.