Oh, the volibear top is actually a favorite of mine (although it's been some time since i've last played it). most build advices i've seen here are pretty accurate, but there's something I haven't seen people mentioning that you should definitely try: Frozen Mallet. An early-mid game Volibear with Righteous Glory, Frozen Mallet and tier 2 boots (Swiftness being my favorite, but Mercury Treads and Tabi are equally good) is a pain in the ass to deal with (especially in low Gold where people are still likely to mess up with kiting). The high amount of HP mallet gives also goes pretty well with Volibear's W scaling, which is a plus. However, it's also important to mention it's rare to find situations in which you can afford to go RG + Mallet right away. The best match up to build Mallet on is probably against Hecarim, as it allows you to mess up with him pretty hard, but there are probably more, especially if you manage to snowball.
Some other build advice for Top Voli:
- Doran's Blade is even better on him than most bruisers, due to W's scaling. It's one of the few champs in which I actually build 2x Doran's due to its early game dominant nature.
- Distortion are core on Voli. Dunno if I can stress this enough, but the reduced CD on both Flash and Teleport helps a fuckton with playmaking
- Sunfire is a good item if you need to shove your lane (against better TP gankers for example), but I'm actually not too fond of it. I usually just ult the creeps if I desperately need to push and build Randuin's as my Armor item (unless I'm against something which requires me to build Armor ASAP i.e. Trynda, Riven and alike, as Randuin rush is too expensive to afford under most circumstances)
That should be it I guess. Try to group up with your team as fast as you can and just dominate the mid game, set up TP ganks with your bot lane (as it's already been mentioned I think). Also, if you can't afford to get an early Mallet, remember that it's a fine pick up as a 5th or even 6th item n_n
edit: formatting was fucked up fsr, fixed