This build was made by me. After months of playing Volibear, I have finally perfected it to my liking. This build was made so that when playing Volibear, you can be extremely tanky mean while doing an immense amount of damage with your 'W' . The large amount of health gained increases its damage making it a great opener for a fight, or a great harass against squishy ad/ap carries.

Passive: When Volibear's health drops below 30% of his maximum health, he will heal for 30% of his maximum health over the next 6 seconds. This passive effect has a 120 second cooldown.
This is a great ability to keep an eye on. It is good to know if it's up or when it will be because it can keep you in lane longer, and is a very effective ability when turret diving. This move has saved my life multiple times.
Rolling thunder (Q): For the next 4 seconds, Volibear will gain 15% movement speed. If he is moving towards a nearby visible enemy champion, the movement speed is increased by 45% instead of 15%. Additionally, Volibear's next autoattack during this time will deal 30 / 60 / 90 / 120 / 150 bonus physical damage and will fling the target behind him.
This is a great item to support and tank with because it allows you to initiate into a fight, then allowing the rest of your team to pounce on the unlucky enemy to get thrown behind you. It is also a nice escape mechanism.
Frenzy (W): Passive: Volibear temporarily gains 8 / 11 / 14 / 17 / 20 % bonus attack speed after an autoattack. This bonus stacks up to 3 times and lasts for 4 seconds.
Active: While Volibear has 3 stacks of Frenzy, he can activate this ability to bite a target enemy. The stacks won't be consumed. The bite will deal 80 / 125 / 170 / 215 / 260 (+15% of bonus health) physical damage. This damage will in turn be increased by 1% for every 1 % of the target's missing health.
This is a good move to use when in a 1v1 fight. It can turn the tables and if you are smart about it can instantly finish them off. Be careful not to Kill steal the AD/AP carries around you with it for it can really screw them up later.
Majestic Roar (E): Volibear lets out a powerful roar that deals 60 / 105 / 150 / 195 / 240 (+60% of ability power) magic damage and slows nearby enemies by 30 / 35 / 40 / 45 / 50 % for 3 seconds. Minions, monsters and pets are feared for the duration as well.
What is nice about this move is that it is a great early game harass and helpful for last hitting multiple minions. It's good to use in combination with your 'Q'
Thunder claws (R): For the next 12 seconds, Volibear's autoattacks will blast his target with lightning that will bounce to up to 3 nearby enemies. Each bolt of lightning will deal 75 / 115 / 155 (+30% of ability power) magic damage and will only hit each target once.
This is a good move to use in any type of fighting situation. It's a great way to deal a ton of additional damage. It's ever better when in team fights because it hits in total 4 people making it extremely effective.

Due to your extreme tankyness, you should take lead into fights with your 'Q' leaving who ever you threw useless in a team fight. Instantly after throwing the enemy back you will want to slow them with your 'E' so there is no chance of escape, or you can use exhaust. I left some wriggle room for the 'W' move. This way you can choose between tanking the damage and doing a large amount of damage leaving the kill for the others around you, or you can use it to last hit champions for easy kills. Early game Volibear isn't very strong, however his 'E' has a nice harass and a good way to last hit minions, although I do not recommend using it too often due to its high mana coast. His ultimate I found was a great way to either farm, or when in team fights. A nice thing I picked up along the way is instead of chasing a running champion, or if you just want to get some easy level six harass off, use your 'R' on minions, the Ultimate favors champions over minions and will chain off to them.

The two summoner spells I chose were for certain laning combos. I figured the ad carry would get ignite and a different spell leaving it better for you to get exhaust . This allows you to get an easy 'Q' off or it can be used to help your laning partner pick up a kill. It can also be used in times of dire need, you can use it to save your partner and yourself. Another reason to use it is when you're solo laning. If you are able to, try and use your 'Q' to throw the enemy into turret range (preferablely close enough for the turret to hit more than once). After that use your 'E' for the slow it gives in combination with your exhaust to keep them stuck in turret range possible picking up a easy kill.

The Items need be in no particular order. The first item Warmogs , and the second item Mercury treads , are highly recommended. The items after the boots (Thornmail ,Force of nature , and Guardian angel ) are all situation items. Depending on the enemy team composition, you'll want to get Thornmail before the magic resist if their team is primarily AD. If they are primarily AP you'll want a Force of nature. If they are even then get a Guardian angel , then you can deiced and whose the most fed character on the enemy team and buy the next item based on that.

Marks I use greater mark of alacrity for the extra attack speed. This is done so that his 'W' charges up faster in fights. I got his great glyph of shielding greater glyph of shielding his greater glyph of warding and his to add to his tankyness. Lastly, his quintessences,greater quintessence of desolation I use greater quintessence of desolation to make up for his damage that he loses getting tank items and runes.