Used this guide to great success... However, one thing I've noted is that it's better to get Frozen Mallet right after Black Cleaver, cause the moment they start noticing you're the carry you're screwed.
Also, I've found Youmuu's Ghostblade a great item for him. Passive gives him move speed for his gatling and the item gives him a ghostblade as well.
*Also, at all you people saying Wriggle's is useless on him: It is AWESOME, simply because until you get phage you get no CC (not counting blind) whatsoever, and Wriggle's helps you attain Lizard and Golem extremely easily. The ward also allows him to farm a lot in safety; you might spend that gold on a B.F. sword but without lifesteal you cannot golem or lizard, and even if you DO have lifesteal you will jungle way slower than a Wriggles Corki.