How I play Darius
first item to rush
Threats to Darius with this build
First of all: I am not a LoL-pro, but I got many experiences with Darius and this item build. In my opinion if you use the start items I recommend you will definitly carry your team.
Why I start with ancient coin? Just because I am an offensive player and I want to harass the enemy champion with my abilities and so I forget to last hit minions and with this item you will earn 4G for each missing minion.
I don't rush black cleaver, because with Phage you will get the extra movespeed + attack dmg and it is more useful to build armor or magic resist to be tanky and support your team more earlier in the mid game.
Because when you are not fed with Darius you will in the team fights and carry your team