This guide has been well tested by my friends and has been used by myself plenty of times in order to test out what is below. The video below is what I have uploaded to youtube which is what will be in this guide just in video format so I recommend you watch the video if you want to see footage of olaf with use of this build.
Play Video

Greater Mark of Desolation
The armor penetration will allow for a higher amount of damage with the damage you will be getting from the items in the build. You will find using these runes you will achieve a higher amount of damage to other players.

Greater Seal of Resilience
The armor gained from the runes will give you a better amount of durability when it comes to the early game and the laning phase and of course will stack the the armour gained later on in the game thanks to the armor in the build.

Greater Glyth of Fortitude
Using these health runes will give you a higher amount of health right from the start of the match which will give you an even play field due to the fact you will find other players get Dorans items so the health will even what you will not be getting due the fact you will be starting with boots. The runes will also help at level two when you take your W that stack off bonus health you gain after olafs default health.

Greater Quintessence of Strength
The runes will give you damage for when you are in the jungle and also more damage as standard from the start of the matches you have with olaf and as you get lower health you will get faster attack speed which will work with the damage to make a fast hard hitting champion from the start.

I take 21-9-0,

Use these masteries as they provide a good amount of physical threat from the Offensive tree and some health aiding durability through-out the match. After testing this mastery setup for a long time with olaf you will be very successful with this build.

So I normally use the build that is stated at the start of the build but there can be certain situations in which you will need to change the order in which you purchase the items to deal with other players but the item build in the order it is in normally works to perfection,

Heavy AP Teams
If you are dealing with this type of team I find that if you take Force of nature before the Atma's Impayler that you will be long more durable when it comes to dealing a team who are AP heavy or have a fed AP Champion.

Jungling Items
I normally use vampiric scepter to start off when I jungle and then take boots after the first run through the jungle which will help you gank due to your movement speed. You are also able to use Cloth Armor and 5 potions when jungling with Olaf but I find that this is not the most effective with this build.

Jungling Items
I normally use vampiric scepter to start off when I jungle and then take boots after the first run through the jungle which will help you gank due to your movement speed. You are also able to use Cloth Armor and 5 potions when jungling with Olaf but I find that this is not the most effective with this build.

Jungling Route
This route works very well for me and I find that you are able to gank at any point on the route if you are on the bottom half of the map you can gank the bottom lane and if you are at the top gank the top lane.

Well thats all I can really recommend but if you have any more questions please feel free to ask question in the comments of the video i linked at the top or in the comments below the guide and I will get back to you as soon as I can. I hope the guide helps you out as the build works very well for me.