This is the build i use when i play Olaf. i only played him for a week cuz thats how long he was on the line up for. i used many different builds and i found getting health then Atma's impaler was a good build cuz of the attack damage, also with starks you got the life steal, the crit, and the attack speed for you and your team.

any rune is good for Olaf but when you get the Frozen mallet you dont need the Lizard king rune. Im not sure if it stacks but if it does you can take it.

Pretty much with masteries it attack damage and crit with some attack speed and CD reduction.

Start with the boots first then work on starks for the life steal. After starks work on either Frozen mallet or Soul Shroud for the health and survivability. Ater you get one or both get Atma's impaler for increased attack damage.

i used to go with the first ability but then i started going for the third one.

Undertow (Q) does damage to all targets it goes through and slows them.

Vicious Stirkes (W) grants attack damage along with life steal and spell vamp.

Reckless swing (E) does alot of damage but you have to be really close to the target. (not good against ranged targets)

Ragnarok (R) makes it so you cant be disabled by anything for 6 seconds.

i go with Ghost for the quick get aways and to get places faster nad Exhaust to slow and blind the target to weaken them and miss you.

This is my build for Olaf it works at lvl 10-13 and after that you will rape everything and everyone that get in your way. comment on it and tell me what you think of it.