Not Updated For Current Season
Long story short, this is a guide how to jungle with Olaf, how to build him etc.
For runes I take armor penetration marks and quints and mana regen per level seals and glyphs. Why? Because Olaf deals physical damage and needs mana to spam that axe constantly in battles, so mana regen will be needed and so the armor pen. With his ulti at level 3 + youmuu's ghostblade you will have armor penetration of 75 which is quite a lot, so you can take down tanks too easily.
For Masteries I have taken 16/3/11, having basic attack masteries in offence, armor in defence (because in jungle armor is good thing to have) and in utility longer neutral monster buffs, the +5% experience gain and the extra gold generation per 10 seconds. When jungling, the experience masteries and longer bufftime is something you have to have.
For items, start withand 5. After getting the 700 gold go to base and buy. After this your jungling is much more faster and effective. Back in jungle, collect gold to buy, maybe gank before that or after that, it's up to you.
Next item to buy is, simply because of the health and damage + you want to build Frozen Mallet later from it. But before Mallet buyfor the damage, critical, cooldown reduction, armor pen and the active ability of the item, orif you want a bit more tanky build. At this point you do quite much damage already, so now it is time to upgrade Phage into. Now you have damage, health and extreme chasing abilities due to Mallet's slow, Youmuu's/Randuin's active ability and the Undertow's slow.
Now it is time to buy more damage and some durability, so buy. It stacks nicely with Vicious Strikes and gives you about 50 more attack damage + critical strike chance and armor. At this point you are going to need more damage, so now it is time to build eitheror, depending on which attribute you are needing.
If the match goes on, sell Wriggle's Lantern and buy.
For Summoner Spells I taketo make it even easier to chase with Olaf and it is good item for ganks.
The secon Summoner Spell I choose is, since it is a good gank-item too.
I dont prefer Smite because it is rather useless especially in late-game. Olaf can jungle without it easily, but if you feel you cant survive without it, leave Ignite and take.
Creeping / Jungling
Then it is time for the guide how to jungle with this build of mine.
I always start from the enemy Wraith camp, because it is further away and it will annoy the enemy jungler if they have one :) Ignite the Blue Wraith and kill it, after that the Lesser Wraiths. Remember, use potions only when you need them, try to keep Olaf's health quite low so his passive is more effective.
Next, go to your team's Wolf Camp and kill the wolves. After that destroy you team's Wraith Camp and little Golems. At this point the enemy Wraith Camp should be back again so head there and kill them and enemy little Golems. Now you should have enough money for Madred's razors, so go to base and buy it. Now it is easy to take down Ancient Golem and Lizard Elder, so consider ganking also in some point.
So, this was my guide to jungle-Olaf, hope you like it. Send feedback or comment and say if there is something you would change etc.