Please note that the build doesn't have to be the same as mine it can have some changes like more tanky build or more attack speed the choice is up to you.I like the full damage Darius so this is my choice .Comments about the build as well as recommends are welcome!

In the firs build (ad carry) build i try to max. the damage i deal.Trinity force grants me the movement speed i need as well as crit. chance for the infinity edge in the late game.Phage in the trinity force grants me the health that i need to not get killed much.
In the second build (AD Offtank) I try to have as much tank as damage so that i can go in first at team fights and kill the opposing team (op Darius).So Aegis of legion grants my team some buffs so it is useful in team fights.

Build 1
-You get a lot of damage
-You get movement speed and crit. chance
-You dont get that much hp
-Players will attack you because they fear you
Build 2
-You have a lot of health
-You have good damage
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Try to get kills in the early game so that you can rule the team fights in late game.If you get feeded you can easily go backdoor or push the mid by yourself .Try to use apprehend yo pull the champions to your turret or your team so that you get an easy kill.