This build gives you the cd reduction, and tankyness, and damage, you need to do a difference
in teamfights, and a little supporting with the starks favor.

i get magic resist, and armor runes, be cause you are gonna get a lot of health in this build, but not the most resistance, and you need attack speed to get your main damage spell off quickly in early game.

i mostly take in the defense three, be cause it gives you a boost in the resistance, and the really nice cd reduction you need be cause all your spells have a massive cd. And i get the attack speed, and armor pene, in offense to really boost the damage of him. And in the utility three, i just boost my summoner spells and the recall time.

Start items: its really just standard solo top items, you need the health Regen to keep you there at early game.

Ionia boots of lucidity: they give the cd reduction you really need early game but if they have heavy stuns, you may have to go mercury treads.

Warmogs armor: it gives really the health boost, you need to keep yourself alive in team fights, and gives a massive boost on your frenzy damage.

Atma´s impaler: it stacks really well with your Warmogs armor, as it gives more attack damage based on how much hp you have, and it gives some really nice armor and crit.

starks favor: its really the item for Volibear it gives him lifesteal, which is key for him in duels and it keeps him alive and he get attack speed, which gives him faster charges on his frenzy making him unstoppable.

Spirits visage: it stacks very nice up with your passive, and your lifesteal, and it gives you extra hp which stacks with atma´s impaler for more attack damage, and it gives cd reduction, which makes you more powerful them you can Spam frenzy.

Youmuu´s ghostblade: it gives you nice extra damage, and the boost speed, of it really help you to reach someone and fling them and it has MORE cd reduction = more spam of abbilities.

Rolling thunder: i max it second be cause the frenzy do a lot more burst at max and it do not do incredibly much to max this skill first.

Frenzy: its pretty much his main damage spell, definitely max this first, it gives Hugh damage and gives him attack speed buff.

Majestic Roar: this skill i max third be cause you only need it for its slow, it dont do hardcore damage, but the slow is nice so just take 1 point in it.

Teleport: its really nice to have, if you are having trouble at top, so you can get back and forth without losing any xp, and you can use it to help your allies. :D

Flash: its mostly just to get the final hit on a enemy, or run away more i cant say.