This is my first build, so be kind.

The first thing you'll notice is that I do NOT put 21 points into the Defense tree. Here's why: The bonuses you receive by taking the quintessential "tanking" talents is relatively inconsequential. Two damage reduction here, 1.5% damage reduction there. When you crunch the numbers, it doesn't really matter. If you receive a critical hit for 500 damage, you're only negating 7.5 points, meanwhile, you've wasted talent points. Instead, I've focused on Volibear's weaknesses, particularly his movement speed and relatively poor gold farming.

Volibear's speed seems, well, LACKING. You have to burn Rolling Thunder to get any kind of speed, and its cooldown makes it inconvenient to use just for the speed boost. The newly reworked Ninja Tabi boots make up for this a little, and also give Voli some much-needed tankiness early game. Also, the 10% damage reduction more than makes up for those talent points you didn't spend. Those talent points, incidentally, have gone into the 4% speed boost in your Utility Tree. This may not seem like much, but coupled with another speed boost from champions like Sona or Gangplank, it adds up quickly. Of course, it's always better to have it and not need it, than need it and not have it, so I've put points into Intelligence for the cooldown reduction. Nothing is more frustrating than seeing the opportunity for an easy kill and not having access to Rolling Thunder.

The gold farming also seems to be an issue. Your primary combo is going to be Rolling Thunder and Frenzy. Unfortunately, you're not going to do much damage with your auto attack until you can pick up Atma's Impaler, relegating you to receiving gold from assists and (few) last-hit minion kills. And since mana-conservation should be one of your top priorities with this build, you really don't want to use your abilities to kill minions. Heart of Gold and four points in Greed help out a LOT in this regard. Of course, you may want to drop Heart of Gold in the late-game phase in favor of something more situational.

I have also put four points into Awareness, because honestly, who doesn't want 5% extra experience gain? This also contributes to early lane dominance. Preferably, this build will be used in a team with no jungler, putting Volibear in top lane with an AD carry.

Since this is primarily a Utility build, I have chosen runes that will hit hard and critical often. Since your auto attack damage is dependent on Atma's, you don't really need attack speed. Movement Speed Quintessences will contribute to Rolling Thunder nicely, especially when coupled with your 4 points in the Swiftness talent. Remember, this build is all about increasing your speed so that there is no chance for an opponent to escape your flip.

You'll recall that we opted out of some of our defensive talents because of sub-par damage mitigation. Ninja Tabi will make up for this with 10% damage reduction from everything but turret hits. This includes minion/monster damage, single target damage, and AoE damage. There isn't a single talent that does all of this. I most often see tanks taking Mercury Treads for the tenacity. I don't really see the point in this, though. If you are the tank, and you get stun locked, are you not still doing your job as the tank to have the enemy team focus you while your teammates dish out enormous amounts of damage? Also, being continuously stunned negates any effect of tenacity, while Ninja Tabi will mitigate 10% of all that damage you're taking while you're stunned. Besides, as the tank, you're SUPPOSED to take as much damage as possible. Being stunned in the middle of the enemy team doesn't prevent you from doing this.

Your next item should ALWAYS be Heart of Gold. 250 health AND extra gold? Yes, please! This contributes GREATLY to Volibear's early-game survivability.

Next is the very obvious choice for Volibear: Warmog's Armor. You know what they say: If it ain't broke, don't fix it. Also, the synergy between Warmog's and Atma's is undeniable.

Consequently, Atma's Impaler is your next item. Build it piece-by-piece, and go back any time you have enough gold for another piece.

Now that we have our speed, health, and damage items, it's time to focus on CC. Frozen Mallet is a must-have for Volibear. Once your Rolling Thunder either flips a target or runs out, you're at a disadvantage. However, even if you can't get close enough to flip your target before Rolling Thunder expires, you are often in range for Thundering Roar. As an AoE, it will only apply a 30% speed debuff, but this should be enough to put some real damage on your target, slowing them by 45%.

Spirit Visage should be your final item. This synergizes nicely with your passive, Chosen of the Storm, and with Warmog's. You will also gain extra AD from the contribution to Atma's, and the 10% cooldown is a definite bonus which you will notice when you're chewing nails waiting on Rolling Thunder to finish its cooldown.

Heal: At first you may think that Heal should be used whenever Chosen of the Storm procs. While you're not wrong about this, you're wrong about this. While it is preferable to use Heal in this situation, it should ONLY be used when you have at least one other teammate with you. If you get stupid (as we all do sometimes) and are caught late-game farming a lane by yourself, it's better to take the death (which is going to happen anyway) rather than waste this summoner spell. Accept the death, learn your hard lesson, and then regroup with teammates when you resurrect.

Ghost: I like to use this both offensively and as an escape mechanic. Combining Ghost with Rolling Thunder, Ninja Tabi, your 4 points in Swiftness, and any speed buffs (Sona, Gangplank, etc.) leads to some blazing speeds which only a few champions can escape. Just try not to waste it on Master Yi or Rammus.

You and your support should take out golems on the way down the lane when the match begins. Coupled with your 5% experience gain from Awareness, this will give you the small boost needed to stay even-level with a solo top, or ahead of the competition with 2v2.

After defeating golems, go through your jungle rather than straight down the lane. Drop your ward at the river entrance without revealing your presence to your lane competition. If they have pushed too far, go for the early gank. If they're playing defensively, check out their blue/red buffs. Often, you can 2v1 their jungler.

After attempting either gank, focus on dominating the bushes. Use Rolling Thunder when you can to drive the enemy back and xp-block them. Often, they will burn their escape mechanic (Ghost, Flash, etc.) rather than be flipped into your AD carry. If this happens, retreat back into the bushes and reset your trap. However, for this to be effective, you MUST maintain your wards. Being pushed too far past the river with no early warning system is certain death, and you have no one to blame but yourself for feeding their jungler.

With the right amount of map awareness and a good AD carry, this play style should let you destroy their tier 1 turret fairly quickly. Now send your AD off to gank other lanes while you solo top lane. At this point, you should already have Ninja Tabi and Heart of Gold. Play defensively, let the enemy push, and then call your AD carry back in for the gank.

Situational: If you are 2v1 when your AD leaves on their ganking spree, pay close attention to keeping your wards up. The last thing you need is to get jumped from your own jungle by some idiot with a death wish. If their jungler comes in from behind you, suddenly it's 3v1, no one is afraid of your turret, and you've just fed three of them. It won't matter if you manage to kill one of them, they still win and now there's no one to defend your turret. At most, you might end someone's spree and get 500g out of the ordeal, but their entire team just got 150g each from the destruction of your turret.