First of all I apologize for my English, there could be some errors ... I think volibear is a very strong champ, not op like some other champ, but it works pretty good. I tried to make that builds as tank as possible because I think is his "strong point".
But let's move on.

Pros

• His passive is very strong.
• Wait, attack speed on autoattack that staks 3 times? Phisical damage that stack with an high % of Bonus Healt? Plus 1% for every 1% of the target's missing health? I think is a very good spell...
• CC which may be useful both for ganks that in 1 vs 1.
• He starts the team fights pretty well with his *(continue on Cons :/ )
• With does damage even if it does a tanking build but he do "tanks" damage while on Cooldown.
• He is a bear in armor that shoots lightning from his claws...

Cons

• He has to be close to his targets to do anything.
• *If the other ADC knows how to play will be hard to take with
• may could have a long CD for his more damaging spell.

I have little to say on this. The Quint of percent health runes are perfect for this champion. Seal of Armor & Glyph of Scaling Magic Resist runes are good for all champ. The Mark of Attack Speed runes are good for Frenzy and Stormbringer to do a bit more damage.

• Thundering Smash don't use it only for gank or in 1vs1... You can use it to escape too and in jungles to move faster. You can use it to take champ under turret to make a kill to the team. Ok, ok... isn't the best thing to do. Anyway you can do it but only if you're sure to don't die.
  
• Frenzy is a good spell, it increases the attack speed for each hit for max 3 stacks. At 3 stacks he can use it to does damage based on bonus health (and voli has a lot ;-) ) and target's misseing health. Keep attention to don't steal kill with this spell...
  
• Sky Splitter Dat fear :O... It's really useful in jungle to take less damage and slows too...
  
• Stormbringer is very strong, 75/115/155 magic damage per hit at 4 targets for 12 seconds with a nice CD... WOW!

We arrived at the end... Volibear is the fist champ from 6300 I bought, and i really like to play him. I can only hope you enjoy this build. Goodbye everyone!