Your Goal with Olaf as my build for AD Offtank is to do all lot of damages and tank your bottom lane too as well.

Items
1: The most important items is Frosen Mallet that give you Health and damage and a slow effect that is really useful in the early gaming and in the late gaming too.

2: Zeke's Herald is really important for you to survive and give you health and CDR (cold down reduction) as well.

3: Sunfire cape is me 3 most important item in this build because you got health and a passive that do magic damage to nearby enemies.

Skills
Your "W" spell is the most important for your survival in late and early game. And it's gives Olaf a damage and life steal buff and that can help you survive a situation that you dies in normal cases. And thats why i max it first.

The second most important spell for me when i play this build is "E" spell and it's because it a good spell to execute a champion fast and thats why i max it last. And this spell is why the health on Olaf is important because it cost a amount of health to use this spell.

The "Q" spell max i last because it only use to slow enemies when the try to flee from you, or take the last health to kill a champion and thats why I max that spell last.

The "R" spell do i take in lvl 6/11/16 as usually, because it's important and a good spell because you can't be slowed and you take reduced damaged for a time!