Hy guys this is my first build, i also gonna say i have a really bad english so sorry if i talk bad.

Olaf for me is one of the goodest champs in League of Legends, he can own every single champ and do an huge help for teamfights .

Pros:
Really good mid/late game.
Have huge damage ( true damage )
Good jungler
Can do pentakills and don't die

Cons:
Early game is a bit squishy
I don't see any more con, he is just great xD

i have chose this skill sequence because Vicious Strikes and Reckless Swing are the champ main skills, for me undertow is only good to kill low hp enemys and to slow them.

I chose ghost and exhaust because they are spells good to play defensive and ofensive.

I chose this runes because Armor pen of marks and quits more olaf's ulti give lots of armor pen and olaf only do true damage all the time, i also put CD im seals and gliphs cause it really help to Reckless Swing and to get skills faster.

To farm olaf is really simple, just trow your axe, go to the minions and atack them with normal atacks, when your like at half hp use Vicious Strikes to regen your hp.

Thank You for reading this guys, i hope you enjoy my build and I also hope you win lots of games with this build :D