Don't buy items in a set order, change things up depending on your team/the opposition.
I'd advise buying Doran's later and letting the HoG tick over while you lane/jungle. Also get Warmog's earlier, it's an item that gets better as the game goes on. Items like Sunfire can help, more HP and free damage while you've got E/R on. Alternating E/W can be more beneficial than simply boosting E since W is a free thornmail with MR included. Also keep in mind that just because you're tanky, doesn't mean you're invincible (unless fed). You can and will die, especially if you go into a 1v5. Feel free to initiate, but make sure your team is around to dish out the damage.
Disclaimer: It's been a long time since I've played him, I don't own him, YMMV, IANAL, I don't ranked, and I have a disturbing tendency to suicidecharge the enemy team regardless of who I'm playing. Use at own risk.