Here is the build that I use when I play Volibear. I've been playing him since he was first released, and out of all the different combinations that I tried, this was the build that gave me the most victories, and still is. Everyone already complains that Volibear is way too OP, so depending on how things go on the battlefield, this build will give them another something to rage about. XD

I usually start off with Doran's Shield, when soloing top, but depending on who you face on the bottom lane, boots/armor and potions will do just fine. Depending on how aggressive the soloing opponent is, sometimes it will be better to go straight into Sunefire Cape before Warmog's Armor for that early armor. I don't really use any critical strike items because Majestic Roar, and Thunder Claws deal enough damage for your team to take the kills when fighting. Even so, Frenzy pretty much does the job for a nice critical shot anyway. If Volibear needs to be distributing more damage in fights, I find that Atma's Impaler works really well with the additional damage from Sunfire Cape.

When jungling, open up with Wriggle's Lantern, but make sure you learn Frenzy first. Majestic Roar can be your first chosen ability at level 1 if it's what you prefer, but Frenzy works a lot better when going after the red and blue buffs. Make sure you have Flash as one of your abilities in case your opponents try to constantly harass your jungle.

In team fights, if the enemy focuses you first and you tend to take a lot of damage way too fast, you can replace Wit's End with Banshee's Veil, and/or Frozen Heart with Guardian Angel. Sometimes, I even like to go Randuin's Omen instead of Force of Nature for the additional abilities in the items' passive. If the enemy is extremely fed and really powerful to take head on, go ahead and get Thornmail for that extra return damage.

I hope you enjoy my build, and hopefully it works well for you. As you read, the six items I chose aren't the only way to go. XD This is my first build/guide, so it's not put together as well or as fancy as most guides on this website... And if you haven't already noticed, I suck at speaking/typing and explaining thing, so no negativity. :P