Darius is a DPS tank character. The idea is to get him Tanky and strong as soon as possible.
Darius is mostly an agressive and will damage his enemy slowly and finish him with his Ulti or will focus tons of damage in a close combat to win!

I chose items to make him a Tanky DPS character, surviving and combat and killing the enemy before understanding what happened, also allowing him to pass from battle to battle in the shortest amounts of time with big amount of health and high health regen.

A dominion guide is added in the last Chapter if you want to try it.

The guide will be updated with the time :)

Why should I choose Darius?

Pros

-Good tank and DPS champ
-Dealing huge amount of damage with no items
-Can gain speed and chase down his target
-Good in team fights
-Good farmer
-True damage-resets on takedown Ultimate
-Can close gaps and prevent the enemy's escape

Cons

-Can be toped in the early game
-A kill stealer ultimate (avoid for the team)
-Mostly aggressive and falls for ganks
-Not ranged and can get his lane zoned
-No cool skins (yet)

Darius is a tank DPS, able to survive in battle the longest and killing or finsihing his tragets with no problem.On my build I focus early tank because I gain enough damage from skills and in the late game I go for maximum damage.

Level 1 - I take a point at Decimate 1st and use it for farming, harassing and killing in the early game.
Level 2-3 - I take Apprehend and not Crippling Strike because mostly I will get a ranged opponent and will want to close the gap between us or just preventing a melee escape.
Level 4-5 - Harrasing getting serious while getting Crippling Strike. Using Decimate at start and Apprehend to prevent the enemy's escape, then you start spamming the Decimate and Crippling Strike untill your enemy is dead. If he ran off with no hp - no worries, Hemorrhage will take care of him, for sure with 6 stacks.
Level 6+ - You just got your Noxian Guillotine and things getting serious. You start with the previous combo and fight through the whole battle, leaving your enemy with OR 160- Health OR 220- With 6 stacks of Hemorrhage. As soon as one of the situations above is happening a quick press to Noxian Guillotine will finish off you poor enemy, leaving you with another strike of Noxian Guillotine for the next incoming battle or the rest of your team fight.

Enjoy your hunt

9 Greater Mark of Attack Damage= Giving Darius head start with high Attack Damage to take his opponents fast and allows and good farm with his Q and passive.

9 Greater Seal of Health= Starting with high amounts of health will give you a free and easy farm while having great damage and big amount of health will scare every enemy champion against you and will let you farm easily and get the kills with no problems.

9 Greater Glyph of Vigor= After every fight with Darius those runes will allow you to heal fast from his wounds and be ready for his next battle, allowing him to be in several battles with full health in short amount of time.

3 Greater Quintessence of Attack Damage= The cherry on the top will give Darius even bigger amounts of damage, letting him being the ultimate Tank DPS.

Why did I chose those Masteries?
The masteries focus on Health, Health Regen, Armor, Armor penetration and some cooldown reduction and damage. I chose every Mastery because:

Defense Masteries

Hardiness + Resistance = Adding some armor and magic resist for our champ (and much better than the other 2 masteries).
Durability + Vigor + Veteran's Scars = Adding even more Health and Health regen to make Darius even more tanky and yo survive more in battle.
Indomitable = Completing 1 point for the rest of the tree.
Initiator = Increasing the movement speed of Darius to close the gap in battle and takedown your target.
Enlightenment = Completing 3 points for the rest of the tree and adding our champ little bit cooldown reduction for spamming your Decimate and Crippling Strike.
Mercenary = Adding points for gold while killing or assisting instead of 1% more damage that we will cover in the Offesive Masteries with Weapon Expertise .
Juggernaut = After increasing Darius's Health, this Mastery add 3% more Health and 10% less disabilities for him to be more active in battle and dominating the fight.

Offensive

Brute Force = Increasing Darius's attack damage by 3 for powerful attacks.
Summoner's Wrath = Reducing the armor of your enemy with the Exhaust for easy takedown.
Alacrity = Filling the points for Weapon Expertise and adding 4% of attack speed.
Weapon Expertise = Adding 10% of armor penetration making him almost unstoppable in the early game.

Regrowth Pendant + Health Potion = For the start of the fight Darius needs to farm and harras the enemy as much as he can with his build, fall back and let his health regen fastly.

Mercury's Treads = Darius will enjoy the normal speed of every champion, low amount of magic resist and a short time for debuffs and stuns allowing him to be active in every Crowd Controled battle.

Phage = Giving you health and attack damage with a bonus to slow enemy's speed allowing you almost a secured kill on the early game.

Warmog's Armor = The item that makes him so tanky, giving him huge amount of health and health regen. Warmog allowing him to survive fights and be ready to the next one in the shortest amount of time OR to survive in team fights while tanking the fight and getting the kills (Darius is a really good kill stealer, for the spirit of the team avoid it).

Frozen Mallet = Adding the Phage "Giant's Belt" making him even more Tanky and to last in battle more.

Infinity Edge + Bloodthirster = Adding our tank HUGE amounts of attack damage and powers for his skills. Also "The Bloodthirster" giving you enough Spell Vamp to help you survive in fights even more and helping you regen from them quickly.

Atma's Impaler = Taking your Health and doing with it something. Darius will get from the Warmog's Armor, Frozen Mallet and Greater Seal of Health alot health and with Atma's Impaler you will get around 70 Attack damage and 70 Armor which never is bad and 18% more Critical strike for more powerful attacks.

Hemorrhage (passive) = Even not in battle you will deal damage, your passive allowing you to make the enemy lose his health while battle or afterwards for the easy finishing blow. Target ran away with small amount of health? For every stack you are doing 5 magic damage for every second for 5 seconds, every hit from your basic attack, Decimate or Crippling Strike will add a stack to your enemy up to 5 stacks on minions and 6 on Champions. Also the passive will give additional damage to your ulti per stack. The stacks is getting damage from your bonus attack damage. A bonus for every stack of Hemorrhage Darius's movement speed is increased by 5%.

Champion with Hemorrhage will make the turret target you!

Decimate (Q) = Your skill for every battle situation. Darius will spin and deal big amount of damage and will make the target bleed for 1 stack. The damage added to your ability is rising according to your bonus attack damage. Decimate has 2 radiuses of attack: The outside for lower amount of damage and the inside for bigger one. Spamming it would be a bad idea because you run on mana and you waste if for no use, for farm it is not recommended but in the fight always make sure you spam it but enough to let you enough mana for your Noxian Guillotine.

Crippling Strike (W) = Crippling strike resets your attack timer and dealing up to 120/140/160/180/200 % of your damage in the next basic attack. Also Crippling Strike slows the target's movement and attack speed for 20/25/30/35/40 %. Crippling Strike cooldown is reduced for 1 second for every stack Hemorrhage the target got. I recommend using it when the target got 3 stacks and above for maximum use and good damage.

Apprehend (E) = This skill does no damage...or does it? The skill pulls the target back allowing you to deal even more damage and preventing his escape. Apprehend can be used for a suprise attack but is recommended for getting your enemy closer to you, preventing his escape and finishing him off. Apprehend passive giving you 5/10/15/20/25 % of armor penetration.

Noxian Guillotine (R) = Your true damage, the skill the making Darius so strong is here. 160/230/340 TRUE damage and bonus for every bonus attack damage you got. Noxian Guillotine's cooldown resets if it deals the killing blow, allowing you in team fights to get more kills with the ulti by spamming it for their deaths. The ability is a takedown and reciving 20% more damage for every stack the enemy champion got. Noxian Guillotine on level 3 with my build and 6 stacks and reach up to 1100 true damage!!!

For all new players or the ones who want to know him better here are few facts about... Noxian Guillotine

-Noxian Guillotine's damage is increased by 20% for every stack the enemy champion got, which can get to 220% total damage!

-Noxian Guillotine's damage is true damage = ignoring any armor or magic resist.
-Noxian Guillotine resets if it was a killing blow
-Noxian Guillotine's damage is increasing per 0.75 bonus attack damage you got.
-Noxian Guillotine damage is 160/230/340 (+ the bonus above) per level the skill got.
-Noxian Guillotine is a finish blow because it resets upon killing blow.
-The animation is cool :P

Recommended

Flash - Exhaust

The ideal combination for the easy takedowns, preventing escapes or running away from battle.
Flash = The easy way to get around, run away from battle or to close in with your enemy.
Exhaust = Preventing any escape and giving you the upper hand in battles.

Useable

Clarity, Cleanse, Ghost, Heal, Ignite and Teleport

Clarity* = For every mana needed players.
Cleanse = Removing all debuffs on the champion and can be used easily on battle.
Ghost = Can be a good exchange for flash for everyone who likes it or for 12- players.
Heal = Can also serve you good in battle.
Ignite = Can do a really good job in finishing the players in the early game untill level 6 that you don't have your ultimate for the takedown. Can help in team fights but not as useable in the late game much...
Teleport = Helps you get around the place easily and back to battle faster (For my picks I take teleport almost in every game in every champion).

Not for use

Clairvoyance, Fortify, Promote, Revive, Smite and Surge

Clairvoyance = Darius is not a ranged champ and has no range skills (small radiuses mostly).
Fortify = Darius is a tank champ and will win the lane in most games.
Promote = Not the choice of most players.
Revive = You are not going to die so it will be useless.
Smite = Darius is a very hard jungler.
Surge = Others spells are more useful than this one.

*People telling me Clarity is not even useful but I found myself mana needed not once. If you kill the Blue carry it would be cool for you

Runes and Maseries are the same because they are good for dominion too and save the trouble to change them all the team.

Tactics

The Tactic is quite simple:
Darius is going to solo top, dealing damage to the enemy and trying to take him down, if you can you should rush to the next point, if you are having troubles you should go back to your point and defende it. Darius makes an exellent defender with him Decimate from minions and champions and can takedown with hims Apprehend and Noxian Guillotine. The rest of the game you should push to the points and defend if needed. According to the build it will be easy for you and you will win with no problems.

Items

This build is similer to the classic build but added more damage and reduced the Health and Health Regen. Build is so:
Mercury's Treads = Starting with the classic boots to reduce debuff effect and small magic resist buff.
Phage = So far the same with the build Phage will slow your target's movement and attack speed allowing you a sweet takedown.
Entropy = Instead of giving him the tanky build at start I start with more damage for winning fights over the points.
Giant's Belt = Instead of another phage we start with Giant's Belt for more Health to survive more fighting your points.
Frozen Mallet = Might reapeting here with another effect but I want to add to Darius more damage and Healh and this item allows it more than the others.
Infinity Edge = Now we are taking, adding huge amounts of damage to Darius making him even more unstoppable.
Sanguine Blade = Adding Darius even more damage and spell vamp to survive more in battle for yours points.
Zeke's Herald = If you will end your build and the enemy's Nexus won't die or they won't surrender for the huge amounts of damage you do in seconds (Which is mostly unlikely), I recommened using this item for more Health and spell vamp for Darius making the game a 100% sure win.

Skills

are not changed much only on level 2 you take Crippling Strike instead of Apprehend and on level 4 you do the opposite.

Summoner's Spells

Taking Ghost and Flash to enter and quit battle quickly, you can change flash with your needs but this is my choice and it works quite well for me - I'm sure for you too.