Hey this is a build that I found to be way useful for me. I think Jungling with Olaf is easy. If you dont like my build well I dont care cause it works fine for me.

Ok everybody is gonna hate because I have no armor and magic resistance and blah blah blah.

If you eat people for breakfast in 4 seconds you dont need armor. And plus when Olaf gets low in health is when he is the best. So combo up his moves and eat people.

Pros
Eating people for breakfast
Extremely good at ganking
Crits almost every hit

Cons
squishy, especially against magic

Ok so in my experience Olaf can be a strong jungler. His passive ability makes him very dangerous at low life. so try to never get him above 50% health when he is jungling. Start off by fighting the wraiths and pop a health potion during the fight if you think you need to but you most likely should not. Next run over to the Golems pop the elixir and you should use a health potion during this fight. Dont forget the usefulness of his undertow but make sure you save enough mana to use it on the ancient Golem. Go to the ancient golem and throw the undertow trying to hit as much as possible. Kill him use whatever health potions you neeed to. Hit the wolves that are right near him now and then start over. when you hit level 2 get his Viscous strikes so that he gets life steal. remember to keep him semi low health. But careful to not get ganked on this. Remember to use smite all the time when it comes up but time it well with his viscous strikes because it gives you an amp on it.
Oh and do not use your W until around level 6 or 7
But when you hit 5 go to the dragon and use everything including your W. But other then the dragon dont use your W.

The reason we start with the Elixir and health are obvious to kill the monsters in the jungle.

But first we buy his boots so that he can help gank people, otherwise your team will hate you for staying in the jungle.
Next we go for Youmuus Ghostblade. This is one of my favorite items dont forget to use its active ability to your advantage. I get this one before anything else because you can use the ability then ghost and then charge into the enemy and gank doing extremely well.
Ok now its the phantom dancer. This is a great sword and I boosts your attack speed. I am an attack speed kind of guy but if you want to go for base damage its your choice because I think if i can hit faster then them I will win.
Then it is Stark Fervor. This is essential for ganking. its aura helps everyone do way better. So therefore I buy it and gank.
Next is Tiamat. This item is new to me and i just added it. I used to go for cloak and dagger or the Trinity Force but this helps you farm and get more money much quicker. It also helps if you are attacked by a bunch of guys, but the trinity force is a very close second.
Last is the Infinity Edge. Enough said we all know how devastating it is.
With this build you should have no problem Ganking and getting the kills.

Oh and if they have heavy magic I normally get the Hexdrinker. It will help alot if theyre heavy magic

Obviously you need smite to jungle but i like to use ghost with it. It helps you gank and get away from a gank
You dont really need exhaust for get away since undertow does that sort of.
Heal is overrated because you rock when damaged
Teleport is dumb because you run so fast
Revive is ok but you shouldnt be dying so dont get it
Cleanse is useless because of the Ult
I am actually pro fortify because its good if your tower is almost dead and your almost there, but it is also good if your almost dead and they want to chase because it makes them shoot twice as fast
Clarity you shouldnt need
Ignite is useless late in the game
Rally is good for ganking but ghost is better
Clairvoyance is just... you can throw the undertow and see if someone is there

In this build you need to follow the skills. go for undertow first because it is the most useful.
Next you need your W to be up for the life steal and spell amp, combo it with smite while jungling.
Next you need to get Reckless swing up and as strong as possible.
When you cant put a point on your E put it on your R if possible if not put it on your Q. Then you will be able to jungle and gank efficiently. His R is not offensive unless you are both going to die. It gives no attack boost so dont use it when you go into a fight. Use it to escape and if its close between you and the other guy use it and youll win because of the defense boosts.

I dont care what you use i prefer attack but others dont, it does not matter to me.