Watch Olaf dance through the enemy lines to the sweet beats of bones crushing and skulls splitting.
This build is what I settled on after trying out the excellent (if more tanky) build by moiseman. I know that adding hit points increases Olaf's damage during Vicious strikes but its not a large enough ratio to warrant using HP in place of dmg items I think. (1000 hp will only add 16 damage while vicious strikes is up...) Instead this build balances survivability with increased damage output and life steal to let you pound yourself to life.
Summoner Skills -
Ghost - This is a great skill for running down and escaping in equal parts. You could replace this with Flash if you prefer, but either way I'd use one of your summoner slots for a movement skill. It will save your life and get you kills.
My second skill is a toss up between Cleanse and Ignite.
Cleanse - I know your ult is already essentially a cleanse, but you will hit plenty of fights where your ult isn't up and you'll enjoy this sucker. Also an exhaust at the wrong time can destroy that lovely balance Olaf strikes up where he barely lives at low hp due to life steal, but this will fix it all up.
Ignite- On the flip side, adding more pure damage to your arsenal can help you get those killing blows on fleeing enemies or help dull the healing of an enemy Taric/Soraka/Mundo etc etc. Nothing is more frustrating then watching a kill slip out of your manly berserker grasp due to heals.
Even though this is a more aggressive Olaf build I still think the defensive tree makes a lot of sense. You will find yourself taking on multiple players at the same time and that extra survivability will allow you to keep on trucking. You can't do damage if you're dead.
Marks: I chose the armor penetration because Olaf already has a lot of flat ArP. The interesting thing about armor having diminishing returns is that it makes armor penetration have increasing returns as you stack more of it (assuming you don't try to drop them below zero). Once you have Stark's and Ghostblade that'll give you 58 ArP which is about a 37% increase in damage!! (if they have 60 armor) You'll essentially ignore everyone's base armor, and with your ult even tanks will have think twice before standing in front of you.
Seals: I love dodge glyphs in general because their defense scales all game. Flat hp are nice early, but physical DPS scales way faster. Seven percent of incoming damage is always just that, plus it can help you entirely avoid gold cards, lich banes and more!
Glyphs: I've always loved CDR in these slots for non-AP casters, and this is no exception. Keeping up vicious strikes continuously is huge, and more nukes and ults certainly won't hurt you game.
Quints: I think you could go flat HP or armor penetration here, but I'll suggest the HP to help you try to get first blood and to generally make you more terrifying early game. You'll have enough ArP through the items and your ult to make the extra 11 you'd get here a little superfluous.
(passive) Berserker Rage: This fun passive allows Olaf to pull off very obnoxious (for the other team) kills where he'll hover at only a few hundred life using his massively increased attack speed to life steal like crazy.
WARNING: Its easy to get cocky once you experience this and you'll start staying in fights at very low HP. There are plenty of characters who can drop a massive nuke or two and end you, so be wary of who's around when you try this trick.
(Q) Undertow: I put one point in this skill early on for the aoe slow. This is not a harass skill with our pathetic mana regen. Instead use it for catching up with fleeing enemies who have broken away from your frozen mallet or toss it behind you (or teammates) to let you escape. Later on if you've got mana to spare or a massive creep wave to kill you can stand alongside the caster mobs and toss it through all of them, then pick it up and toss it back through again. That should slaughter them all!
(W) Vicious Strikes: This staple of a skill should be activated continuously in any major fight. Aside from the obvious fact it makes Olaf hit damn hard and get a large boost to his life steal, it also makes Undertow hit harder and helps refund some of the HP cost of Reckless Swing. GRRAAAAAAWWWWWW!!
(E) Reckless Swing: This skill isn't fancy, but it doesn't need to be. Run up to your foe and blow off 340 of their life. Wait a few sec. Repeat. Just be careful to not seal your own doom with an overzealous use of it.
(R) Ragnarok: Going into a berserk rage, Olaf stomps all over the poor chump standing in front of him. The key to using this skill is to actually wait and use it later in the fight when they think they have you. Suddenly their attacks will be merely tickling you, and with your ridiculous attack speed and armor pen you'll chew through their wet paper protection. Of course if you're getting a ton of CC dumped on you as you flee a gank or are initiating one then using it earlier certainly isn't bad. If its just a straight up fight, however, save it!
Playing Olaf and Choosing Items -
Depending on who you're laning with and who you think you'll be facing you can either start with a Doran's Shield or a Health Crystal. The crystal will get you to Phage faster, but that's not going to help if you have to keep leaving your lane to heal up and miss out on experience and gold.
If you've got a lane mate with good CC then you should feel free to go for first blood. However, be careful early game since you have no built in escape skills. Its painfully easy to step a little too far forward and get your *** handed to you. On the flip side of that, a lot of people don't realize how much damage you can dump out as you approach death; if you're in a fight that doesn't seem to be going your way and you won't be able to escape try turning around and dropping one of your attackers. Take them with you and die like the hairy rage fueled man you are.
You can also harass anyone less tanky than you with Reckless Swing, but be sure you don't walk into a trap.
Hopefully when you get back to base after level 6 you can purchase your Berserker Greaves and/or Phage. If you didn't take cleanse and the other team has a lot of casters or CC, then Mercury treads are a great set of boots too. Once you get just those two items combined with your ult you'll already be a scary melee machine. You can keep pushing your lane, hit the jungle or look for enemy characters who have over extended themselves. If they're not turret hugging you should be able to ghost out and slow them with undertow. Then nuke them with Reckless Swings and run alongside laying into them with Vicious Strikes. If you think they're going to hit you with some CC or they reach their turret then activate Ragnarok to keep on trucking. Again, remember that you have no escape skills so be aware of how hard you are committing.
Mid Items:then finishand
After getting Phage and boots you'll want to get want to get the Vampiric Scepter next. The extra life steal is awesome and also means you'll no longer have to rely on spamming VS to get your life back. From there you have to decide whether or not you need the slow and HP of Frozen Mallet or the AS/ArR of Stark's Fervor. Those will be your next to items, but the order is up to you.
Now your team will probably be getting into some serious team fights. Your general strategy in these is to pull partial aggro from their team. You're not tanky enough to absorb a whole pissed off team, but if you don't get hit at all you won't be much of a threat. This often means being the 2nd one into the fight and sprinting for their squishy DPSers who depend on CC to keep them alive. If you can try to target anyone who'd be able to insta-gib you at low hit points (Garen, Veigar, Annie, etc) so they're out of the fight by the time you're down there. Once you start to draw off fire from your teammates activate your ult and finish pounding your target into the ground.
Late Items:then eitheror
Your strategy won't change much from here out, the next items just make you better at it. Ghostblade helps your attack speed before you've been injured and lets you dash around a fight easier in case your target has a built in flash/dash. Also the CDR will help you keep up VS as much as possible. Oh, and more armor pen to demolish your foes, wheee! Phantom Dancer will help keep you in a fight with its dodge and the extra move speed and crit are an obvious addition. Banshee's Veil not only lets you shrug off a spell and keeps you safer from caster insta-gibbing, but the extra hit points and mana are help you stay out in fights for longer.
Thats all for now! If people have any questions/comments post them below and I'll respond ASAP. Thanks in advance for any feedback!
Celebrate Techno Viking with DJ Steve Porter's Remix: http://www.youtube.com/watch?v=Jf13MmZIcLs