I picked him up about a week ago and have been experimenting w/ builds. I think I found one that works pretty well.
Start: flask,pots, ward First back: Giant's belt and Philo stone, boots (may take 2 trips but the giant's is more important to rush) Next get Brutalizer so they can't ignore you. Finish Warmogs. Now you have some decisions depending on situation but I usually try and grab Shurelyas->atmas
Late game finish your Black cleaver and if you're up get a last whisper. You are now a tanky monster put on the map specifically to kill ADC's and then turn and wreck the rest of the team since you will still be at half health.