Once ago, I was playing a normal match and I decided to try something different.
So Counter-Pusher Olaf, as I like to call it, was born.
Everything you'll have to do if you're using this is to stay on lane 24/24 and farm minions and push.
Ignore teamfights and run from ganks like hell.
Usually, after he/she breaks your tower, your opponent will start roaming and fighting.
You wont. You'll farm and push to hell.

Armor cause armor is good.
Magic resist. You'll need this for the sneaky mid will try to stop you.
Attack speed. The more the better. Faster pushing = moar gold.
Movement speed so you can run from those jealous players that cant stop your awesomeness.

Fury - Moar attack speed = faster pushing.
Deadliness - Damage / level. You'll always be the highest level so..
Havoc - % damage increase. Why not.
Brute Force - Moar damage.
Summoner's Wrath - Moar speed for our Ghost.
Butcher - Moar damage to the minions = faster pushing.
Destruction - Increased damage to turrets. Perfect.

Durability - Health / level just as damage / level.
Tough Skin & Bladed Armor - Damage reduced and reflected back to minions and from them. You'll find yourself alone without minions around most of times as they are afraid so you'll need these.
Veteran's Scars - Flat health. The moar the better.
Hardliness & Block - Flat armor and champion basic attack damage reduction for those bastards will try to stop you.
Safeguard - Turret damage reduction. Cookie.

These are essential. You will need them to escape any incoming ganks and they work just great with your ultimate.
This is one of your core items. Not only that it gives you and insane pushing ability with the passive that strikes more targets, but it also gives you movement speed that is essential for easy escapes.
This item is just perfect for this build. Movement speed + active so you can run from anything + health and mana regeneration so you can stay even more than your enemy on lane.
Attack speed, health, mana, attack damage, movement speed, critical strike chance. Nuff said.
Damage to the minions around? Yes please. Health and armor for any incoming enemies? Yes please.
Health and armor? Same thing as + an amazing AoE slow. This item is just in case someone somehow catches up with you. Just pop it and away.

Undertow - Your main pushing ability. Enemy minions will be just crushed. Max it as soon as possible.
Vicious strikes - Life steal, spell vampirism and damage? Yes please. You will max this ability second. Its very usefull for sustain and damaging turrets - cookie.
Reckless Swing - If anyone tries to stop you use this. The insane damage will force him/her back. You'll max this ability in the end for its not that usefull to what this build is made for.
Ragnarok - Getting ganked by 2 or more players? Later noobs. Works amazing with any speed buff or item just as or .

Ghost - This is essential. Cooldown on ultimate? Cooldown on items? Keep this for situations like that and use it to escape.

Teleport - Enemies are all at mid or bot? Teleport to one minion on top for faster and safer push. Also you can use this to escape if you dont have anything else. Just teleport to a turret from your base though it might not work in early levels as the enemies can kill you.

Well this is it. Not so long. Not so complex. Use this only when you want to have fun.
Its not a good build for a serious game or rankeds.