Volibear is a great champion, but if you want to be a real menace you need your masteries to be on defence. Why? Because Volibear needs health for Frenzy damage, and also you got higher regeneration rate, and thats a good thing when fight start and everyone will attack you.

As for items, I would start with dorans shield, berserkers graves, warmogs armor, madreds bloodrazor, infinity edge. With doran u get hp and regeneration, witch is good for start and also it enables u to attack and possibly kill your opponent at lvl 3. Berserkers give you standard speed and attack speed, witch is crucial because u will get Frenzy faster. Warmog hp and regeneration, witch means more damage with Frenzy, marders for speed and damage, and infinity edge for damage. After that, you can make anything you want.

I start with rolling thunder, then frenzy and roar. With all 3 you can attack and possibly kill opponent. I then get Frenzy and roar at level 5 with no ultimate. That will allow you to get more damage quicker and there wont be any mass fights until level 12 or higher. Rolling thunder is the last ability that I take to level 5, because even with level 1 you can get to your opponent and take him down.