Well first of all, I think Darius is one of the better champs. With the right setup, he can take down health quickly and keep the enemy champ by his side to get killed. This build is to make Darius the strongest of them all. Typical AD setup at the start with the I.E and Phantom Dancer, but with the warmog's and atma's you get extra health and damage. When seeing you, the other people on the team will be scared and run. Once they do this, you are doing this build right.

I made those runes for damage, damage, and even more damage. At the start of the round, you want to maybe get a kill or two. Using your Q and these runes will either kill the champ, or bring their health down a lot.

For the masteries, I wanted damage and some defense. Simple as that.

Again, these items start off as an AD carry build, but later will give you great health and damage buffs. They don't make you invincible, though, so be careful if you are under leveled.

For the skills, you want to get your Q to max pronto. It is one of your best damage dealing attacks and if used properly, you will easily harass the other champ and maybe kill them after a bit. W is next priority, and lastly E. Get R whenever possible.

For your Q, you want to get enemies and champs at the end of the swing. Near the center, it does less damage. At the edge it does 50% increased damage and after maxing out at lvl 12, you can creep farm easily and get a lot of damage on champs easily.

Your W will be very useful, mostly for slowing them down. It recharges fairly quickly and if the other champ is running away, use your W on them. It is also a good way to start a fight. It gives bonus damage and with your Q, it does great things. The bonus damage will also work on turrets, which is a great addition.

E. Darius's E is so great. It starts fights wonderfully, gets champs that are running away, and it can save your teammates lives if they are being chased. You want to use it sparingly, though. It has a long recharge. You want 1 point in E at the beginning for all its pros at grabbing champs, and it also has a good passive.

His Ulti is also great. It's a finisher, so don't use it willy nilly. When your opponent is running away, you can use his ulti and if it kills, it will instantly recharge.

Here is how I use my skills:
To START a fight.
E > W > Q > R (if low health)

When teammate is IN A FIGHT already.
W > Q > E (if running away or about to kill teammate) > R to finish if possible

When champ is RUNNING away.
E > Q > W (to slow) > R if possible

Pros:
-Very strong, even early game
-Great E
-If used correctly, his R can be a game changer
-Can turn a team battle upside down
-Can save teammates lives (w/ E)
-Good at getting turrets

Cons:
-Most people who play Darius are too ballsy. They run into battles thinking they will win when they might not
-Somewhat slow at start w/out boots
-Slow attack speed

If used correctly, Darius can easily make a game. Also, his R is INCREDIBLY satisfying when you kill an enemy champ with it.