Many of you probably thinks that it's stupid to not go for armor pen. Well, it might be stupid too but I've decided to go a different build anyway.
So instead of doing a little bit more dmg via armor penentration I crit a hell lot more even from start, which can be pretty awesome :3

Even though this is a dps build Olaf still has very high survivability through his ultimate and high movement speed together with 2.8k hp.

The skill sequence isn't very surprising, but here we go

Ghost - Undertow - Ragnarok - Vicious Strikes - Reckless Swing - Undertow - Reckless Swing - Undertow and of course Vicious Strikes asap...
A tip is to hold down Shift so you can throw your axe and use Reckless Swing quickly enough to still keep your normal attacks going since both Undertow and Reckless Swing will have very short cooldown. You will be able to constantly use them while hunting someone.
Remember that Undertow is just for the slow and to never go in a fight without Vicious Strikes - it is what keeps you alive in those tricky moments.

The play style is the same as for all dps Olafs; choose one annoying bastard and focus the **** out of him/her, recommended to go for the dps carry such as Ashe, Ezreal or Ww. Once your target is down you simply change target or go home. But remember that when you have low hp you do a lot more dmg, so even if you are hurt you can still surprise someone from a bush or behind a corner and regain very much hp very quickly thanks to Vicious Strikes.