Well, this is my first guide, so maybe this will be a fail, but I supose that this will be, at least, useful. Just one thing before starting, I'm spanish, and the english level here is veeeery low, so maybe I'll make a few mistakes.
Wll, let's get started!

This guide/build will be focused more in early and mid game, because late game depends much on the champions on the ally and enemy team; also, this is a jungler guide, and the early game is very important for the jungler, so I'll focus on it. Just remember that this guide is designed to gank a lot, because i really think Volibear's true potential is his power to gank like hell, kill an enemy and continue jungling or go base to use your money.

So let's start with the guide!

Just go like a normal jungler: boots and 3 potions, go from blue to the golem camp and gank bot if it's possible. If not, I jsut keep jungling.

Normally I go to kill the wolves and then I gank another lane, but if it's not needed just jungle more until you take the Phage to gain HP and a little AD, and that sweet passive that will be so cool if you keep ganking. Next of course is to take Mercury's Treads, you can also take Berserkers, but unless there's a full tank on your team it'll be better if you choose that tenacity.As a tank, your next choice is to be tanky, so Giant's belt, chain vest to get armor, and Warmog, and let's start filling it while you take enough money to buy the Frozen Mallet, because 700 HP is a very nice number, plus 20 AD and that passive... And then you'll have to take Atma's Impaller to see your AD go up and up and up (not that up, but meh) and those criticals will be funny too combined with your passive attack speed. From now the thing can change depending on the game, but a Sunfire Cape is allways welcome, and it gives you more HP, whic means more AD, and more armor to be even more indestructible (remember, you're a POLAR ARMORED BEAR), and the magic damage passive is allways funny when you're a tank who can take the enemy back and slow it so he stays more and more time at your side and your cape does the job for you.

The Force of Nature isn't REALLY needed, but if there's a magic enemy too fed it will grant you more time at battle, and my favourite part, when Warmog and Force of nature are combined you transform into a Dr Mundo with his ulti activated, which means that you're an indestructible monster (not that indestructible, but killing you won't be a party for the enemy team).

The runes I've chosen (i have to say that I only have the seals and the gliphs for now) are focused on increasing Volibear's effectivity (Doe sthat word even exist?)

-Armor seals: Man, you're a tank. You need armor. Besides, these runes will help you to keep your passive down until you do the first gank, you'd prefer not to use it against the two golems.

-Cooldown per level: At te beggining you don't need too much cooldowns, you're jungling, an these runes will give you more CD reduction at late game than the other ones which give you 0,6 (or something like that). Of course you use the CD reduction because Volibear becomes deadliest when he can bite you more times per minute, and the Q and the E sure are annoying on teamfight, so using them une time and another is allways good.

-Attack speed marks: I don't think i really need to explain this, you just want to bite the enemy the faster you can, and attacking more times per second means doing the killing blow before the enemy goes back to the turret.

-% HP Quints: Volibear's W increases his strenght depending on your extra health, so more HP means a deadliest bite on you enemie's ***, and you're a tank, so more HP won't be bad. And remember that your passive uses % of max HP too.

EDIT: Cool, I used this rune build and they make my jungling much easier, and now i don't need to worry about taking more aattack speed n late game. It works, guys!

I think that if you guys just pay atention at the skill sequence for a few seconds you'll reallyze that what we want to do with Voli is to deal the maximum damage we can with the W and to slow the maximum we can with the Majestic Roar. Rolling thunder's really use is only to take the enemy behind you so you can use your E, slow him and attacking him 3 times. And that's it, the next thing you'll have is a nice lunch (unles your enemy is a Sion, or an Urgot... i don't think those guys are very tasty)

This are tank masteries, of course, and some of them will make you able to keep that passive until you do the first gank. The next is easy, normal tank masteries, more armor, and that, and the extra HP is allways useful with Volibear's W and passive (nut much, but hey, that enemy carry won't escape again with 10 HP)

It's easy: your midder does the pull on the golem, you kill it (remember, you take first Majestic Roar to fear the monsters aand take less damage) and then you choose to learn the W. Next step is to attack the wolves (of course using the E) and using the W's bite to kill fast the red wolf. The wraiths are easy, use your W too to kill the last one with one hit and go to the golems, then use Smite on the little one and kill the other combining E and W. Before that you can start fanking with your Q and E and finishing with W, or if you're not sure you can go to base, buy your shoes and start eating enemies. I suggest to use ghostspeed to assure you kill the enemy on your ganks.

PROS
-Jungler Volibear ganks like hell, and if you keep doing it the game will be easy.
-You're almost indestructible on a 1v1, and with that massive amount of HP (remember, you have 350 more HP that the data up there say because of the Warmog, and much more AD because of Atma's passive) you'll resist a lot and bite like a ****ing crocodile.
-You're a tank, but you're fast, so entering teamfight from one side won't be as dangerous as with another tanks (and remember, you're a good initiator)
-Your healt regen at late game will be so epic that just with going out of the battle for a few seconds will make you recover a nice amount of life

CONS
-The wards, if the enemy puts wards your support or even you will have to take oracle or the pink ward so you can gank without problems.
-Your magic ressistance isn't very high until you take Force of Nature, so if the enemy midder feeds fast you'll have to change the item sequence.
-Ghostspeed is a good choice for ganking, but at late game it's not the best choice, so it can be perfectly replaced by Flash.
-If the enemy ****s your jungle at the beggining you won't be able to gank fast, which means that... well, it's allwayss a bad thing.

Well, I hope this Build/Guide will be good enough for the Volibear players here, it works on my hands, and I'm not a pro player, so hey, if a high ranked player uses it and it works... Yeha, then I'll be a ****ing genius!
Well, nothing more, good luck, summoners, may the armored polar bear be with you