Hi folks.

Its my first guide so plz be gentle.

As i have been playing lots of games with irelia and came to a few conclusions:
1. She is not tanky enough
2. She doest deal that much sustained damage after inicial burst.
3. Either you sacrifice your survivability, burst or sustained.

After trying out lots of builds mostly tanky i wasnt satisfied with those 3 points above.
So what can we do?
As she beneficts a lot by AS and also by CDr, she needs some health too, as you will be going to be in the middle of the battle.

Pros

-Great burst
-Great sustained
-Nice survivability
-Great duelist

Cons

-If you play smart she doesnt have many
-You can be insta killed if all team targets you

All you can ever need

You begin with 31 ArP (with masteries)
16 armor (with masteries)
14 magic resist(with masteries)

After you buy The brutalizer you get 46 ArP and you wont need more.

Not realy much to talk about.
I choose 21/9/0 cause i feel confortable with it, damage, resists and HP.
Improved ghost and ignite.

In the beginning i used to play ghost, exhaust but, i learned with experience that ignite is better.

Ghost, chase enemies and run from them.

Ignite, finish him and healing debuff (if used smartly, can turn the tides of a duel)

Some other spells like flash ignite would be ok, its up to you.

Now the interesting part.

Last games i have been playing her assasin so what do i need?

Begin with Dorans blade(health damage and lane sustain).

Now depends on how well you are doing but on my first trip back i always try to get full boots.
Why not CDr boots? Cause you will get capped with other items and potions.
Magic resist and more tenacity is awesome.

Next i go for the brutalizer (damage, CdR, and ArP) all of these fit you perfectly.

Now go for trinity force, depending on game tide i choose what i buy first but i usually buy sheen and phage first.

You should be starting to feel like you miss some AS, so go for Wit´s End starting with Recurve Bow and then finish it.

You now have what i call Irelia complex, well dont be greedy, you already have burst and sustained damage so what can i do to improve all of her assassin stats.

I then buy Zeke's Herald, a not so common item for most players but i find it´s stats perfect.
AS/CdR/Heath/Life Steal, this baby has it all.

You are now beefier, and feared by enemy team so play smart.

I finish with some more health, more AS and a decent passive from Ionic Spark.

Conclude your Yoummuu's Ghostblade.

You are not as tanky as most of the builds you see yout there, but believe me you will survive with tons of regen from AS, your ulti and low cooldown stun and Bladesurge.

You will find this build is cheap, i finish it most games.

LVL 1

Blade Surge
I usually dont go for first blood but if the chance comes i try not to waste it. Blade surge can easily take half a skishy's health (with no health item). Just farm.

LVL 2 n 3

Hiten Style
Nice true damage on hit, and decent HP regen.

LVL 4
Equilibrium Strike
Now you can start to harass (be wise and try to land your stun)

LVL 5

Hiten Style

LVL 6

Trancendent Blades
If the game is even you should now get the advantage.

My priority goes Trancendent Blades, Hiten Style, Blade Surge, Equilibrium Strike. WIth this i get max damage first.

Tried prioritizing Equilibrium Strike and but the outcome wasn't very pleasing.

Not much to say here, i tried to jungle her but she's just not that good.
To get the most out of her go solo top, mid should be fine too, bot its just decent (depends on both team combo).

Bladesurge will do your farming effectively and safely.
Usually don't waste mana on Hiten Style unless to damage a champion.
She can easily get to level 6 to 10 in lane cause of your great regen of autoattack and ulti.
Plus in most situations enemies wont risk a tower dive because of your stun.

As all assassins, try to time your entrance well, if you don't, you risk beeing obliterated by spells/ultis.

Target carries, Burst them down as they try to flee =) and get back to fight choosing the next best target.

You will get their attention, be sure you are not caught in some major stuns, roots and ultis (Malzahar, Amumu, Nunu...Veigar's combo...).

You should always build according to game tide and your team needs.

The Cherry on top of the cake.

I dont have stats and im to lazy to get prints but lets do some simple math.

Your total AD shoud be 180 (112 base 60s bonus)at 18 with brutalizer and Trinity force, reember Wits end? so our burst so go something like this just with Bladesurge.

Burst
Bladesurge 140+180=320
Trinity Force 450
Wit's end 42
Hitten Style 75

Burst AD
770(assuming 75 and your 46 ArP, target shoud now have 29 Armor and ignore +/- 25% of AD)
So 770+0.75=577.5 = 577

AP damage
42(with 30 magic resist and the same 25% magic resist)
42*0.75=31.5 = 31

True Damage
75

To sum up your burst will do something like 683.
(this seems a litle low to me but lets continue)

After your burst, by order i try do use Stun/slow 280-25%=210 plus 410 true damage from ignite, pop your ulti and finish them with 160+40(from AD)=200x4(blades)=800-25%(armor reduction)=600.

Dont forget one or two auto attacks.
Assuming one:
180AD*-25%= 135
31 Wits
75 Hiten
=241

Assuming 2 Auto attacks
*2(autoattacks) = 482

Finally
With all this, within a few seconds you will be doing:
Burst 577
Stun 210
Ignite 410
Ulti 600
2 Autoattack 482
=2385

If you have baron and red buff you are godlike.

This is just math, you try it out.

Try it out if you have doubts.
Constructive criticism is welcome.