First. yes i suck at making these so any comments or questions would help

Volibear should be played based around health items for his 2 main abilities. his passive and his W - Frezy. with this setup with a few changes i make to it depending on machups you should be able to tank and 1v1 most anyone in first half of game and do very well in second half.

The Reason behind these items and alternate routes for them depending on your role and game.

(your boots are always based on who is carrying them/there most dominating type of champion/who your laning against)i.e. Merc for AP, Ninja Tabi for AD

There are three ways i build items on volibear the list above is the most current and what i have found most effective.

Warmogs/Boots/Frozen Mallet/Warmogs OR Sunfire cape/Banshi veil or Thornmail

Rushing my warmogs starting with the pendent to last in lane. the reason for this is your main attack W has a ratio of 20% of your life. you will not realize how strong this is untill you use it with any large amount of life. aswell your passive will heal for an additional 300+ life everytime it is active from your warmogs.

Frozen mallet? not ryleas? yes. your abilities cooldowns will stop you from using them alot and you will be auto attacking with your W's passive really fast and more often than your skills. it also grants you 700 life which again i cant stress how amazing this is with your passive and W.

After this point you may decide on your next few items based on your opponents. who is carrying them (check score) if an ad champ is pulling the team like crazy i grab a sunfire cape then a Thorn mail. if AP? i grab a banshies veil. if you are doing fine as is i suggest a sunfire cape then another Warmogs.

by the end of the game you will have 6k+ life (+ 2000 more life when your passive is active) and your W should close to 50% most champions.

Alternate item routes
boots/Philosopher's Stone/Heart of gold, than build into Shurelyas for CD-Regen-life/into a Warmogs of Frozen mallet, then finally into a Atmas
i also use this build without an atmas but its your choice.

Why not Atmas in your other setup?
i stopped using atmas because i was using my W more for the kill than the auto attack, and found i am more often the "tank" of each game. if you wish to use it i would suggest grabbing after warmogs and frozen mallet for the early W damage.

*Force of nature is also another nice item if need magic res due to your high health for regan. a must in some games (ap controlled)

*witts end is also a choice you can take if you feel u dont have the attack speed for team fights + ult. if you keep your stacks up on minions you should be fine though.

Passive - Chosen of the storm
When volibear is at critical life he heals for i think its 30% of his health at a very rapid rate. late game he heals 100+ health every .5 sec (roughly :P ) This has a 2 min cooldown and if you can only start fights when you have this ready. it catches them off guard as well as yourself sometimes

Rolling thunder (Q)
when active he runs faster for a few seconds, if targeting a enermy champion he gains more speed. when he reachs them he flips them over himself, i get this at level 3 and max last, using just to catch up to players

Frenzy (W)
Frenzys passive places a stack every time you attack (stacking up to 3 times) for each stack he gets increased attack speed, 8% per stack at level 1.
Frenzy has an activation attack with around 15 sec cool down that deals damage + 20% of your health with addidtion 1% bonus for each 1% health they are missing. (same type of effect as Garens ult if you have ever used him) this will pretty much finish off anyone with 25%-40% life once you have your warmogs or frozen Mallet.
i max this first for the increased attack speed and heavy dmg it does (your main source)
(use minions to keep your stacks up in a 1v1 if there moving away and back in. you cannot activate without 3 stacks)

Majestic Roar (E)
sends out a wave around you fearing all enemy minions and damaging and Slowing enemy champions. added damage off of AP which i do not use. i max this second using it to clear minion waves and slow running enemies.

Thunder Claws (R)
all of your attacks while active cause chain lightning to hit all near by enemy targets. level whenever possible. use in every team fight that you can and to clear minions waves (when it is needed) this also has an AP ratio but is not needed

R > W > E > Q

Leave up your Q for chasing and ganks (when they run it will allow you to catch up fast to use your W to finish or continue the fight). after you fling them use your E right away to slow them down even more from running. since you are gaining attack speed from your W keep attacking untill they are around 25% which is when you will activate your W (it has a small range so keep the Q open and ready to finish them off)

i have been using flash and exhaust to keep further control over any opponents whether its lowering there damage or teleporting on them to land the finishing blow

i play a 0/23/7 mastery tree setup to be as tanky as i can be at the start while only stacking health items and staying in the fight as long as possible. just personal preference.

for runes i am using
armor pen Quints
Def and magic res with health
you can also sub in the health quints but i do not have them at the moment and find that the armor pen is working well with my W

if you are in lane agasint a Volibear a few things i have learnt from using him. do not rush him unless you have used up his Passive (120 sec cool down) unless you have heavy burst damage like garens ult to finish him off.
be carefull of his W's damage. if you look like your up in the fight it can almost half health you for the kill. around 15 sec cool down and HAS to have 3 stacks
ignite rapes his passive so keep it handy

so far i have not played volibear agasint another one who does aswell and for the most part i have a much better kill/death then any other i play. early to mid game with this setup you should be able to 1v1 most champs by keeping stacks up and saving your skills for when they run. in team fights remember to use your ult and E to hit them all which will be sure to score you double, triple, and up in kills in team fights. i play him as a tank and initioator but its up to you once you learn how to use him. there was more i wanted to add to this but its 6am and im tired so i hope i didnt miss anything major, thank you for reading (if you did) and i hope this helps someone! comment and let me know what i am missing

*be carefull of the ignite!