This is Martellato (EUW), and I'm going to introduce to you, one of the Deadliest and most Effective Darius builds ever. This guide is still under construction. Your comments will be strongly Appreciated.

Here's a quick list of terms and acronyms used throughout the guide:
AD = Attack damage
AP = Ability Power
AS = Attack Speed
Ar. Pen. = Armor Penetration
M Pen = Magic Penetration
LS = Life Steal
SP = Spell Vamp
CRC = Crit. Chance
CRD = Crit. Damage
HP5/MP5 = Health/Mana per 5 seconds
GP10 =Gold per 10 seconds
CDR= Cooldown reduction
Nuke = Champion who deals a large amount of damage within a very short period, then waits for cooldowns
DPS = Damage per second, Champion who deals damage over time through auto attacks
CC = Crowd Control (slows, taunts, fears, stuns, snares)
AoE = Area of Effect

• Darius abilities are not item reliant.
• Darius passive Hemorrhage works like Ignite, Reduces the cooldown of Crippling Strike on Consecutive attacks and makes your Noxian Guillotine deal twice more damage when stacks.
• Decimate is a great farm, good damage and at the same time short cooldown period.
• Crippling Strike hell lot of damage on basic attacks!
• Apprehend, gives 25% Armor Pen. which will be upheld with other Armor pen. items.
• Noxian Guillotine Deals a very high damage and can be cast times.
• Hemorrhage Stacks to give you movement speed buff.

• Noxian Guillotine can be baited by heal or extra health abilities.
• Mana champion.
• No Hard CC.

Greater Mark of Attack Damage

- My personal Favorite. Gives a fair early game damage boost. that lets you build Boots or Cloth Armor and not to worry about your early damage output.

Greater Seal of Armor

- Top Lane Match-ups follow early physical damage (by basic attacks) and some Magic damage later on when they level up their skills.

Greater Glyph of Scaling Magic Resist

- Since AP casters gain Damage over time, with Scaling Magic Resist, you get a higher, more effective Magic resist mid/late as they buy AP items.

Greater Quintessence of Armor Penetration

- Good Boost of Damage until you get your Apprehend.

Why Decimate First?

• Decimate Gives you AoE damage that helps farming. Also deals a fair amount of damage with no delays of basic attacks. Also an escape mechanism with the movement speed bonus. It's spammy and with each level, the cooldown is reduced. Therefore it's reasonable to get it first and prioritize leveling it first.

Why Crippling Strike Second?

• Crippling Strike Has a speed debuff as well as its extra damage, is spammy and Helps you get earlier kills.

Why Max Apprehend Before Crippling Strike?

• Apprehend gives 25% Armor Pen. as passive, which helps A LOT in fights against those tanky solo top champs until you get Last Whisper that stacks with your Passive armor penetration to sum a total of 65% Armor Penetration. The Slow of Phage/ Frozen Mallet will make you needless of the passive on Crippling Strike, However after you level and max your Crippling Strike, the rival champs can barely move which is a great chase/escape mechanism since you have AoE ( Decimate)

Is probably the most common Summoner Spell among League Summoners. It Saves you from really dangerous situations. So it would be my First Choice on Darius

SPACE

Is Great against champs with lots of life steal or Hp5 like Aatrox/ Dr. Mundo, Also secures your kills and helps you get those defensive play-under-the-turret players.

SPACE

Teleport helps you gank and cancel Shen's Ulti and similar. Also lets you back and lane and not getting your turrets down.

SPACE

Can be used both defensively and offensively. It doesn't work well against champions suck as Olaf, Master Yi, Garen or Irelia But if you start to fall behind, it still deals a attack damage Debuff and gives you the opportunity to fight against them.

Defensive Items:

HP Items:

• Frozen Mallet: - Gives high amounts of HP, fair amount of AD and a passive that is necessary for Darius.
  
• Sunfire Cape - Wouldn't be my first choice but I've seen Dariuses building for the sakes of the HP/Armor.
  
• Warmog's Armor A lot of HP that can be matched with Atma's Impaler and makes you tanky while giving you meh amount of AD!

Armor Items:

• Randuin's Omen: This item, is a great item to be used in escapes. (Movement speed debuff), Fair amount of HP and Armor, making you super tanky.
  
• Atma's Impaler Matches with Health items like, Warmog's Armor or Frozen Mallet, and gives you AD for 1.5% of your maximum health. Armor as well.
  
• Frozen Heart This goes very good against AS fighters like Olaf or Jax, it gives CDR and a lot of armor also helps getting rid of Mana Hunger.
  
• Thornmail: This item is a counter to DPS champions like Tryndamere so buying it is really conditional and depends on your enemy team composition.
  
• Wriggle's Lantern A classic early-game item that in addition of giving you AD and armor it also gives you the ability to farm minions and push the lane a lot faster. Also you wont need to buy Sight Wards all the time.
  
• Guardian Angel As a Fighter solotop champion, this will go great on you. If you get in a Team fight and suddenly your team backs off and you're stuck; No problem, as this item is Reviving you, you have the time to think how to escape!

Magic Resist Items:

• Maw of Malmortius: I personally love this item. It gives a lot of AD, A lot of magic resist and a Shield that wont easily let you die.
  
• Mercurial Scimitar: the Ragnarok Item. Easy to escape enemy CC with this item also get attack damage.
  
  
• Wit's End: A classic item to benefit fighters with attack speed. You see this item on Shen all the time. It's Also good with Darius for faster stacks of [Hemorrhage.

Boots:

• Boots of Mobility: I've seen this item on similar champions like Talon. It makes you mobile and lets you gank and help other lanes.
  
• Ionian Boots of Lucidity: If you decide to build this item, keep in mind that CDR cannot go beyond 40%!
  
• Mercury's Treads The best Tenacity item in the game. Amazing against those with a lot of CC.
  
• Ninja Tabi: Good item against champions like Olaf or Tryndamere that don't have a solid CC and are DPS.
  

No1. Jax: As mentioned earlier in the guide, Jax is a champion with AS passive ( Relentless Assault) , therefore items like Frozen Heart would come in handy. Also Jax deals Both Physical and Magic Damage, so Maw of Malmortius / Wit's End would be the best offensive items against Jax. Any HP Item is OK, Armor and Magic-Resist items are strongly recommended, specially Frozen Heart. Best boots would be Mercury's Treads against Counter Strike.


No2. Irelia: Irelia is a Defensive kind of champion that builds Lots of HP and Armor. Because Irelia's main damage is Physical damage and it's not an Attack-Speed champion. Armor items like Thornmail, HP items could be really good. For the heal on Irelia, You can build Executioner's Calling Early game. Best boots would be Mercury's Treads, against Equilibrium Strike.


No3.Cho'Gath: Cho'Gath Always builds a lot of Armor/Magic Resist and a lot of HP specially, thanks to Feast. Therefore a little Magic Resist like Wit's End or Maw of Malmortius and then Ar. Pen. items such as Last Whisper, is also very good. Best boots would be Mercury's Treads against Feral Scream.

No4. Darius: Darius Has all of his damage dealt Physically (Except for Hemorrhage that is nerfed enough for anyone to actually care). High Armor, HP and also Ar. Pen. items are great against Darius. Keep in mind that Darius is a GREAT duelist. Last Whisper is also really good. Best boots would be Ninja Tabi.

No5. Olaf: Olaf is also an AS Fighter, therefore Frozen Heart is very effective. Watch out for Undertow and Build items with high AD and high LS. Best boots would be Ninja Tabi


No.6 Nidalee: Nidalee can be shut down early. Build offensive and Guardian Angel. if Nidalee gets fed, learn her style of playing and decide whether Armor or Magic Resist. Always stay close. Best boots would be Ninja Tabi / Mercury's Treads.


No.7 Jayce: Jayce is specially squishy and mana dependent early, so try camping and shutting him down. Try to attract him in team fights and watch out for Thundering Blow. Against Jayce you need to build defensive specially Armor. Keep in mind to ward everywhere for the poke. Best boots would be Ionian Boots of Lucidity.


No.8 Malphite: Even Though Malphite is tough, he doesn't deal a lot of damage. Building high AD and items like Last Whisper is effective against him. Make sure you have as much Tenacity as possible. Best boots would be Mercury's Treads.


No.9 Riven: Watchout for Ki Burst, stay away and proceed while its on cooldown. Since Riven Players max Ki Burst first, means her other abilities are for late game. Build Armor/HP and AD items. Last Whisper would be a great help. Best boots would be Mercury's Treads.


No.10 Teemo: Go offensive against Teemo, If It's AP Teemo, buy Maw of Malmortius, Wit's End; Otherwise buy Frozen Heart, Randuin's Omen. Best boots would be Ionian Boots of Lucidity.


No.11 Singed. Build offensive items, stay far and don't engage in fights near enemy turrets, or you will be Flinged. Last Whisper is effective. Best boots would be Ionian Boots of Lucidity


No.12 Zed. Try building balanced, HP/Armor/AD, Items like Trinity Force are good. Also Frozen Mallet+ Maw of Malmortius. If the enemy Zed has other benefits, don't forget Guardian Angel. Try to confuse the enemy with putting your shadow near enemy's, and dodge the Razor Shuriken, Try Camping and Ambushing to shut him down. Best boots would be Ninja Tabi


No.13 Shen. Shen doesn't deal much damage. so try building against just like Cho'Gath. Last Whisper or Bloodthirster helps you getting the kill faster. Best boots would be Mercury's Treads.

Thank you for reading my guide, I hope it did help you in any way or at least gave you some new ideas. I'll be looking forward to receive your feed backs. This is Martellato and I wish you a great time playing Darius. Please send me (Via PM) a screenshot of your results playing with this build and I will add it here with your name.
Once again I thank you for your time and patience,
Love you all,

Martellato.