(I made this for a few friends, but I hope it helps some of you, if you are interested in a new build for a fun champion. In addition, this is BASICALLY half-done. Any input would be good :D)

Why Attack Damage?

Let's clear up something very quickly: Darius can tank, but he can TRULY shine as a high damage dealer. What lets Darius do damage that most heros can't is his E's passive. While other champions need to go and grab a Last Whisper to fight tanks or counter that annoying thornmail, Darius's passive 25% armor penetration allows him to just tack on even more damage.
I will say this: Darius's earlygame as an AD can be annoying against a good enemy jungler. While you move faster, you have less HP to survive a gank, and are just less durable than your tanky build. However, Darius's endgame as AD is unimaginably strong. An AD Darius can pump out more damage than an AD Carry, is more durable, and has slows, a pullback that counters flash when timed right and his Ult is the single biggest chunk of True Damage ingame. Another fun fact about Darius is his passive in conjunction with his Q. With two Phantom Dancers, you alreadyhave a move speed of 510+, but if you pop your Q in a teamfight and hit enough enemies? It will skyrooket up to 600+. Even Rammus will have trouble outrunning that Darius. On top of this, because your job is to run in, kill the AD Carry/AP Carry in 3 hits and cause as much mayhem as possible, the enemy team is going to do this: Because of your massive damage endgame, they have a BAD set of choices to make:
1) Focus down the Darius and let the AP Carry and AD Carry on your team do their thing: Destroy them.
2) IGNORE the Darius and allow him to run around like lumberjack, destroying everyone on their team.

However the BEST part, in my opinion, of being AD Darius? You do MASSIVE damage, 3shot even the tankiest of champions, and above all else? you can go WILD with your ult! Do you remember the last time someone cried when the AD Carry got fed? Oh, right, the enemy team.

Why NOT tanky?

So, why AD over Tanky? Endgame. Engame Darius as a tank is ineffectual at best. His abilities do little damage compared to characters like Riven. However the worst part of all of this is when you're a TANK, because of your low output, when you use your ultimate, you plan to KILL with it so you can use it again, right? WRONG. Taking kills with Darius as a tank is pointless and the same as a Lee Sin taking kills: It does NOTHING for your team. Who cares if the tank is fed? He's not doing anymore damage. He's going to toss that gold into more HP/Armor/Magic Resist and the end result? So now you have a Tanky Darus that takes little to no damage and has a lot of HP. You have no way to stun and the only way to save a teammate is to either kill the attacker or pull them off with your E. However, your E has a decent cooldown and, as a tank, you do no damage. When the enemy Ashe is just dishing out damage, what can you do to stop her? You're a fed tank. She's going to ignore you and focus down your friendly carries, all while you flail your axe ineffectually against her lifesteal.

For an AD champion, the masteries don't make much sense, right? You'd be surprised. As a melee AD, you can get focused and bursted down fast, even in a 1v1, regardless of your damage. The tanky masteries give you a sturdy earlygame, allowing you to run in and poke, having both the advantage in health and damage reduction, returning fire against you will prove unfavorable. However, the masteries really come in handy towards endgame, where, without a single health item, you will have 2.5k HP. Not too shabby for an AD carry build. While you swing your axe like a zealous madman, dealing 700+ crits twice a second, healing 300s, other champions will find it hard to do the same damage with your flat damage reduction and higher-than-average health.
In conclusion, the entire point of the tank masteries is to allow you to survive a burst from most champions and live in situations where you would otherwise have died, and let's be honest, you're playing DARIUS. You don't have to worry about narrow enemy escapes, you have your passive. Tick, Tick, Tick, DEAD. +300 gold! It's far better to be on the safe side earlygame and not toss the enemy team kills. Worst case? You have 150+ farm when a team fight breaks out, meaning you have at least two items in your build, meaning you'll be critting 300+ at worst. Then the joy of your ult comes slamming down, ensuring you get fed and they rage. You don't have to be FED as AD Darius to be scary. Play like Karthus: Mouseover, click and press R.

Items and Why Early ATS

I'm sure the first thing everyone of you were thinking when you looked at the items was this: Why early attack speed instead of a bloodthirster? The answer is easy: With a Zeal and Zerker Greaves, along with a lifesteal scepter, your earlygame may be squishy compared to most AD Tanky tops, but that isn't the goal. As a Darius poking, you want to be able to rush in, do a Q and a melee, and get OUT. The attack speed is INSANELY helpful once you reach 6 for one reason: Your ultimate. For every auto attack, you apply one stack of your passive, and for every stack, your ult does 20% more TRUE DAMAGE. Taking almost 400 True Damage at level 6 is a LOT of damage, and even if it isn't a killing blow, it's bound to greatly throw the fight in your favor.

Pros:

- Extremely Potent Endgame Damage
- Farms well
- Pokes well
- High Move Speed, Attack Speed and Lifesteal make killing you harder, even without armor or health items.
- If they choose to focus you, which they should, they will need to stun/ult you to keep you from out-lifestealing their damage. This means your other teammates won't be taking flak.
- Can Easily solo Baron with only 1 bloodthirster.

Cons:

- Vulnerable to a stunlock burst.
- No Natural escape mechanisms.
- Can be focused down
- Cannot lead a charge.

This will be short and sweet. Darius is strong. He can chase down most champions easily, can pull someone who flashes over walls back, do insanely high damage and forces the enemy team to play defensively during teamfights. The enemy AD Carries and AP Carries won't be able to be anywhere near you. You oneshot them. They have to hang back, but even then you are a big threat to them with your E and flash. Darius is the squishy killer. He is on par with the strongest assassin champions ingame. Merely being there in the teamfight gives you a presence much like a Talon. Squishies FEAR you. You can take them from full to nothing so fast they can't do anything. Meaning they will treat you one of two ways:
1) They will panic and ignore focus targets and try to burn you down to protect themselves.
Or
2) They will run away from you if you move towards them. This is a very effective method of shutting down enemy carries. You don't have to kill it to keep it out of the fight.

If you know you're going to have issues with the enemy top lane? Play defensively. You don't HAVE to go for early kills. Darius is hard to poke because of the range and size of his Q, and the earlygame damage it has. While you CAN kite a Darius, most Solo tops tend to have weak ranged pokes, and have to come to YOU to hit you. That means you can Q before they even reach you, W when they do and walk away before you take much damage.

Warding and Pushing?

One of the most IMPORTANT things to NEVER do as Darius, especially as AD, DO NOT GET BAITED. During laning phase, especially earlygame, you have NO NATURAL ESCAPE MECHANISM. You have flash and even that isn't a get out of jail free card. The downside to this is how HARD your champion can push lanes, and how much faster you can clear a wave than other tops. Your Q is a AMAZING farming skill when used right. However, when a Rammus or Olaf comes trundling into your lane from jungle with double buff? The worst thing you can be doing is fighting or pushing lane.
You get counterpicked? Don't PANIC. Get an early Philosopher's Stone if you're getting outlaned by poking, and PLAY PASSIVELY. Just because your champion is a CHASER and AGGRESSIVE by design does NOT mean you need to roleplay it out! You have good burst? Not worth dying for to prove that you do. You can run faster than most? So can Olaf with ghost and ult up. JUST because a kill seems easy doesn't mean yo should dive it! The FINE line between a good a bad Darius is what they dive. Here's a small list of DOs and DONTs:
DO:
- Play safely. Buy a ward everytime you back if possible. It's better to sink 75 gold, equal to 3 minions, into a ward so you can keep farming minions than to be dead for 20+ seconds AND the 15 seconds it'll take you to get back to lane just because you don't want to ward. I'll do the math for you here: 75g for a ward, or lose 6 minions (150 gold), At Least, while you walk back with your tail between your legs.
DONT:
- Do NOT push lane when your jungler isn't nearby. If you know for a FACT that the jungler is watching you? Go ahead. Be a little daring, push your lane and try to draw them out. If the worst case happens, your jungler can rush over and bail you out. This is a TEAM GAME. Don't let the fact you have a strong duelist champion delude you, the enemy jungler IS aware you have no escape mechanism. He IS aware when you have no flash. AND he WILL camp your lane even if you get counterpicked if you play aggressively.

Darius is dependent on farm, just like any other AD Carry. However, you have a lane to yourself. However you play? Remember this: A Champion kill is only 300 gold, and in total, gives less P than a creep wave or two. Two creep waves is worth the same amount of gold, and is far less risky. Let me give an example of a game I had:
Enemy Riven: 2/1/0 99 CS
Me as Darius: 1/2/0 150 CS
I got shut down by the jungler. I got overconfident and got ganked twice. So why is my CS higher? Riven gets overconfident with her item advantage. She stops CSing and tries to kill me over going for minions. I ignore her play extremely passively and do nothing but CS, abusing my Q for last hitting. End result?
Riven's gold: 2x300g + 99x25g = 3075g
My gold: 150x25g = 3750g
Champion kills are NOTHING BUT STEROIDS for earlygame. They don't mean you win your lane. NEVER forget to kill as many minions as possible, and try to safely zone your enemy. Letting them push ALMOST to your tower is NOT A BAD PLAN. They have to follow you past midlane, fight you close to your tower, and going in for CS is dangerous with your E. Not to mention ganks from the enemy jungle aren't going to come and you can get ganks freely.

As AD Darius, how should you work with your team? Function like any other AD Carry. Target the squishies. However, Darius has a special role as well. Cause AS MUCH CHAOS as you can. Randomly pull in the Soraka and make her panic and use her abilities. Charge the AD Carry and harass it. Hell, pull the tank over to you and away from your allies! You are a high damage AD Carry. But you ALSO have the ability set of an OT. Get creative! As long as you cause damage and turn them away from your AD Carry? Don't worry if you die.

I'll fill this out in detail later.