This is a recreational build looking to exploit Olaf's passive and W. It will, for obvious reasons, not work in a variety of games. When it can be executed, however, it will be hard to die.

Because this build offers little defense, armor and magic resist runes are necessary.

It's best to fill your offense and utility tree - to keep things things running smoothly I used TheOddOne's mastery guide.

You can change the build order as needed or throw in a few different items, per the requests of the game (you may need a Force of Nature or Quick Silver Sash if the AP is really hitting you, or a Frozen Heart, Frozen Mallet, Warmog's, or Thornmail if the AD is becoming a problem). The more you build away from this AS/LS guide, the more you will need to build Olaf normally and the (substantially) less effective this build will be. It's on the edge of being effective as is, but again, it's a recreational build.

I recommended starting with Q to offer poke if needed, then following with damage output normally. Once your build starts coming together, focus on your W and then your E. The W is essential and the E will deal substantial damage and amp up your passive.

Exhaust - The slow and damage reduction has vast utility. You can use it for your target or to block out a pest in a team fight (the list goes on).

Ghost - Get in or get out.

Teleport - Fantastic for split pushing, getting to where you need to be, or taking out the minions. It has an array of benefits for this build.

Flash - Flash is flash.. You could probably do without it, but it is still a decent summoner's spell.

I would recommend any combination of the first three.

Don't forget this is a recreational build, or you'll screw yourself. The main function is to aggressively return life by means of heavy life steal and attack speed. This will keep you in the game, whether you need roam and charge briefly or your in the middle of a fight.