I agree with the guy above, FM isn't optimal for Olaf anymore, and the same for your mastery tree. This builds just doesn't give me anything for reading it.
A tip is to think outside the box, try different builds and items, Wriggle's Lantern is a very good item on Olaf, i recommend it.

I got totally different thoughts. First off starting items. Cloth Armor and Health Potion x5 is superior to any starting items, be it solo top or jungling Olaf. Elixir of Fortitude and pots is better actually but it doesn't build into anything.

Your build is old classic build which used to go hard in early Olaf's days. Simply, Warmog's Armor is better then Frozen Mallet. To be honest, I did recommend long time FM over WA, but I realized with tons of games that it's not. Of course it has perma-slow and that is what Olaf needs, but simply you won't be able to survive enough long as you're getting focused hard.

Berserker Greaves are decent boots, probably good choice as you don't build any attack speed early, but it does buff AS by a minor amount, while Mercury's Treads and Ninja Tabi are much more effective.

Trinity Force is not bad item on Olaf, but I wouldn't recommend it along with FM.

Olaf without Ghost? I don't simply see how it could be replaced by Flash. Olaf is similar to Nasus, means he is no type of a champ who deal damage and gtfo quickly. He is beast, poppin Ghost and melting faces all around. Definitely Ghost is better.

Lastly you masteries. Offense tree is weak *** hell when compared to utility. Olaf is a champ which benefit from utility hard, Archaic Knowledge ? Lol.

I got totally different thoughts. Check out my quick blog Olaf build and see my way.