I played him once, by instict. The way to play him came easily. What you need to know is that he's a TANK and an HYBRID. 2 spells are better with AP and 1 with AD. His ULTI can't go higher with AP or AD. His passive makes you gain a lot of HP (30% of his MAX HP) when below 30%. 1 spell is better with HP (FENZY). FRENZY makes you gain a lot of ATTACK SPEED, so you don't really need to buy some.

Focus on 3 items for TANK and 3 items for HYBRID. Boots of ARMOR or MR are the best choices. WARMOG'S ARMOR is the main item. After that, choose your own by instinct or by how the game is going. This build makes you gain 203 AD, 84 AP, more than 4000 HP and about 50 HP REGENERATION. Also, it grants you around 100 MR and 130 ARMOR. For runes, I choose 9 SEALS of ARMOR, 9 GLYPHS of MR, 9 MARKS of HYBRID PENETRATION and 3 QUINTESSENCES of HYBRID PENETRATION. Take 9-21-0 as masteries, gaining HP, HP regeneration, ATTACK SPEED, AP and AP PENETRATION.

To play him, it's simple: start with a Doran's Shield, go bot (if possible) and take Frenzy as first spell. Slay minions and harrass with the active of Frenzy .

Later, chase away the enemy Champions with the Thundering Smash and do some AoE damage with your Majestic Raor. Use your Stormbringer to destroy huge minions waves, in a team fight or to finish rapidely an enemy champion.

My last and only tip is: wait until your passive is done before rushing into deep combat, when using it.