Please see my other builds and vote!Thank You!
Go man and kill they.Go and drop beams in their heads.To a ULTRA KILL!

RECKLESS SWING:
The Reckless Swing is the most importantly skill to kill enemies with Olaf.
UNDERTOW:
Slow enemies is good to kill, Undertow dont have one good attack in enemies more you can use to slow and kill.
VICIOUS STRIKES:
When you're need kill quickly one enemie use this skill, is good to kill quickly because your attack speed bonus.
RAGNAROK:
Use when are destroying tower to no run the risk of is stunned or snared.

RUNES OF ARMOR PENETRATION:
Armor Penetration is good to Olaf because he need have to take more damage in their skills.
RUNES OF HEALTH:
Health is good to Olaf.Olaf dont die easy to the enemies when have health, so you made Warmog to help in your health.
RUNES OF ATTACK DAMAGE:
Attack Damage is the most importantly with Olaf, your skills is moved by Attack Damage.Attack Damage help take more damage in Undertow skill.

GHOST:
Ghost have a big use in the game, good to escape and good to kill.You can use too for go to help your team in team fight or other things.
IGNITE:
Ignite have a big use too in the game, is good to kill the enemies when they have low health.While you up level your Ignite spell damage increases.

Team work is the most importantly to Olaf kill, friends of slow or stun can help he slowing or stunning enemies to he kill.The team can help Olaf be feeded, when Olaf is feeded he kill quickly all the enemies quickly.
Destroy turrets is importantly in the game, Olaf is a great destroyer of turrets.So while he are destroying the team need defend he, or the team can help destroying the turret to be more quickly.