UPDATE 21/10/2011!!!!

Added the "situational items" section

Hello everybody, i've been around Mobafire for a while, mostly looking up for builds for those champs i never played before or barely ever used, to check for skill order and strategies. Now i feel like i could contribute with a guide on the champion i use the most: Irelia, the Will of the Blades!
This build is created for a solo top play, i almost never played it in a duo lane and i don't recommend it since Irelia needs a lot of farm to become a true juggernaut. Laning with a support is a waste since your spot should be covered by an AD carry, jungling is kinda slow on her even with true damage and life steal from Hiten Style, mid is simply a bad idea. Solo top is her spot, and that's the place where you can play at her full potential.

Let's take a look at this champion together, feel free to comment and give your tips and advices, they are always welcome :)

To get a hint of what we are talking about, i suggest taking a look at the official champion spotlight, even if a little outdated, and played in jungle and a different overall setup.

PROS
+ Good sustainability with Hiten Style
+ Bladesurge is one of the best gap-closer of the game
+ Awesome CC reduction with Ionian Fervor
+ Stun and slow
+ True damage with Hiten Style
+ Excellent last hitting ability with Bladesurge
+ Transcendent Blades can vanquish easily a big wave of minions, deals lot of dmg in teamfights


CONS
- Very item-dependant
- Kinda squishy early game
- Transcendent Blades can be dodged easily
- Doesn't represent a big threat for beefy/armored enemies
- Requires some skills (and bravery) to use her correctly

This passive is what makes Irelia almost invulnerable to CC, especially in teamfights where it can reach the incredible amount of 40% reduction, stacking with Mercury's Treads

Some may say this is the skill to max out first, but i personally recommend the opposite, leaving it as last, maxing out Hiten Style and Equilibrium Strike first. The reason is that the first one is essential for your lane-staying power and because, for harassment, is just better when combined with an eventual slow-stun from Equilibrium Strike. However it's a great last-hitting tool, so i recommend placing 1 point in this at lvl4.


This is what Irelia it's all about: sustainability and true damage. At lvl5 this skill gives a nice life steal, especially combined with Wriggle's Lantern, and 75 true damage per hit. Add a Doran's Shield and a philosopher stone and your HP won't go down so easily!


The 2nd priority skill on Irelia. You should remember that the stuns comes not only when your health is lower but also when it's equal to your opponent's. This leaves lots of opportunities when opening a fight, saving Bladesurge for chasing and catching up with an enemy (or as a coup-de-grace on very low health enemies lol)

The typical harassing sequence i use is:
opening with Equilibrium Strike ==> 1-2 hits with Hiten Style ==> chase down the enemy with Bladesurge ==> land another hit with Hiten Style.

As usual, runes are personal choices. I personally use:

• Greater Quintessence of Health: 78 extra HP that are always good for laning. If you are more of a daredevil you can go for greater quintessence of desolation, or whichever quints you prefer
  
• greater mark of desolation: kinda mandatory runes for any AD champ
  
• Greater Glyph of Scaling Magic Resist: mres/lvl glyphs are my favourite choice on almost any champion. Past lvl9 they equal their flat counterparts Greater Glyph of Magic Resist and at lvl18 they give an amazing 24 mres boost. Maybe not much on a tanky champ, but can come in handy if you still didn't finish your Force of Nature, while early game your regen/life steal should be enough.
  
• Greater Seal of Armor: since we are playing solo top, more than often we will find AD based champs (with some exceptions ofc), so boosting up early our armor, combining these with Doran's Shield can makes us really sturdy since lvl1.

Masteries are focused on utility and defense, leaving the offense tree at 0 points because we are building a sturdy, sustainable champ, not an assassin nor a carry. Sustainability in lane is essential, since you will get harassed/ganked a lot. Extra armor and magic resistance from Hardiness and Resistance are always a good choice, Strength of Spirit kicks in when you get your Trinity Force. Utility masteries are pretty self explanatory...mandatory points on Spatial Accuracy and Blink of an Eye . I don't pick Greed since it's 1g/10sec means 240g in a 40min game, and that's just...low.

Note: summoner spells are really a personal choice, this is just what i felt better with, not necessarily the best choice for Irelia.

TOP TIER SUMMONER SPELLS

Invaluable tool for escaping, good also to flash closer to an enemy and instantly Bladesurge to them. Overall my favourite summoner spell. I tried experimenting with Ghost but that just didn't work out for me.
Since we are laning solo top, staying in lane is vital. Recalling in the wrong moment might be fatal to our tower, compromising our whole farm. This spell will let us recall just when needed, and be right back to farm.


Other viable choices:

Exhaust: if my team really needs one. Overall a very nice alternative to Teleport, useful throughout the whole match.
Ignite: kinda meh...but still viable option if you are a really aggressive player.
Ghost: some people prefer this one to Flash for its chasing opportunities. Tried it myself, didn't work out very well, i'll just stick to the flash, but feel free to try it!
Smite: planning on jungling? Mandatory spell, since Irelia is already a slow jungler (with amazing ganking abilities though)


Just no:

Cleanse: Ionian Fervor and Mercury's Treads are more than enough
Heal: do you really need it with all that lifesteal?
Clarity: philosopher stone should be enough if you don't waste your mana on wrong Bladesurge
Fortify: that's for *******, use your blades to defend your tower!
Rally: ...
Revive: bad troll is bad

The most controversial section of the whole guide may be this one.

STARTING ITEMS OPTIONS

- My favourite starting item. Armor boost, hp regen, +120hp. The only -big- downside of this choice is that it doesn't build into anything. Best choice for balanced players. Replace it mid game with a Giant's Belt
+ 1x - 2nd viable starting option, since it builds directly into philosopher stone. You will lack armor and hp, but it's more suitable for a defensive playstyle
- Might feel like a good choice to someone, since it gives a nice dmg boost. 3% lifesteal gets lost in your Hiten Style passive. Not recommended, but can work out sometimes. Nice if you like to play aggro.
+ 5x - Carebear start, but makes you really really hard to be taken down early game. Builds directly into Madred's Razors
+ 1x - Meh, i don't like this start, only pick it if you are REALLY confident on being not harassed, or if you are not really good at last-hitting.
+ 3x - More suitable for a mid player, still a good choice if you plan on harassing and chasing often, or if you like mobility overall.


MID GAME
By mid game your build should look something like this:

= = PHILOSOPHER'S STONE = = =
OVERALL BUILD COST BY NOW: 6850g

Gold/sec items like philosopher's stone and Heart of Gold grants a constant flow of money, combined with nice health and regen stats. 30 mins with these two means and additional 1000 gold, and they will stay just until late game when you will sell them for more defensive items. Giant's Belt builds into Warmog's Armor, Phage instead will build into the MANDATORY Trinity Force. Wriggle's Lantern is an excellent item for lane-staying power. Armor, life steal, a free ward to protect your flank from ganks. It will stay until VERY late game, when you will be able to change it into an Atma's Impaler

LATE GAME
Ok so we reached the crucial moments of the battle, time to turn Irelia into a real juggernaut!

= = = = =
OVERALL BUILD COST BY NOW: 11310g

By this time Irelia has become a fast-moving tank. We reached more than 3000hp, 160+ armor, 150 mres, 150+ AD. We sold our gold/sec items to bring up our resistances in teamfights, completed our beloved Trinity Force and Warmog's Armor. If your match is going particolarily well (or it's just damn too long) you may achieve Nirvana, and finalize your build, becoming the DOMINATOR.

ENDGAME BUILD
Behold...

= = = = =
FINISHED BUILD COST: 15865g

Just by seeing your completed build, your enemy will be like "ok what do we do now?" Our champion (considering a full Warmog's Armor) has reached 3600+hp, 220+ armor and mres, 215+ AD and 480 movement speed. 480. A fast-moving, undying juggernaut that will make even the hardest champion shiver in fear.

Thanks to all those who commented and gave their opinion about situational items. I'll list down some viable choices if the enemy team setup requires some adjustment in the item build!

My main early game setup is intended for the majority of cases where you find AD-oriented champions, like:
Udyr
Yorick
Gangplank
Talon
Riven
Nasus
Renekton
Garen
Irelia (orly?)

But there are some nice solo top champs that are AP oriented like:
Singed
Rumble
Mordekaiser
Galio (my second favourite champ :P)
Twisted Fate
Nidalee
Cho'Gath
Akali

Pretty much the ones i have seen solo top more than once in all my career. there are some others left out but they almost disappeared from the threat-list.

Laning against AP champs is not much different from AD, speaking of item build. Rushing mres is obviously the best choice.

If you feel like playing without wards slots, you can easily do a simple switch:

==>

or

==>

This will turn our early game build into something like this:

= = PHILOSOPHER'S STONE = = =

or

= = PHILOSOPHER'S STONE = = =

As a personal choice i would go for the Wit's End path, overall worth all the golds. Eventually you will replace it late game for something better, but it really depends on your playstyle. And depending on your playstyle, you can experiment with the item build.

Keep in mind that the MAIN CORE must always be:

=

Feel like going more DPS? You can build something like this:

= = = = =
FINISHED BUILD COST: 15875g

Feel like going more SUPPORT? This can be a creative alternative:

= = = = =
FINISHED BUILD COST: 15195g

If not the best, Irelia is among the favourite solo top champions. Fast, sturdy, self-healing, with a good burst early game. Watch out for ganks! An underfarmed Irelia is just a burden to the team, and an easy kill for the enemies. Map awareness to avoid ganks is vital, exploit your high mobility and Bladesurge to reach for the squishiest enemy champion.

Playing with Irelia is tricky, since her stun relies on her having lower hp % (NOT flat hp, %!!) than the enemy. With health items it means that even a lower percentage of hp, compared to their carry's, means a really higher overall amount. An almost guaranteed stun.

Abuse of Transcendent Blades, since they have low cd. Extremely powerful tool to push minion waves and deal aoe damage in compressed teamfight.

Feel free to experiment and drop your comments to improve this guide. Please avoid random downvotes and try to explain why you disagree with this guide ;)