Well guys, this is my first build, so feel free to comment it.

This is my way to play Irelia.

Pros
Great damage
Good mix of Magic, Physical and Pure damage makes you hard to counter.
Mana effective
Quite team undependant
Good health regen even without lifesteal
Great farmer
Not that vulnerable to CC due to passive
Good melee dps that can deal damage even when blinded
Good CC
Easy combo (W>Q>E>auto attack....>SPAM R)

Cons
Squishy early game
Cooldown dependant early game
Dependable on kills/killsteals/assists
Almost all itens are expensive (exept boots and hexdrinker)

I take 21/0/9 to make she a easy killer and great farmer early, mid and late game.

I always take Ghost, to escape a gank or to reach someone to kill, and Ignite, to make some kills when they run and mine skills can't get at them.

I often take Exhaust, it's a good choice to reach someone faster if you use Ghost and Exhaust and it's nice when you use Exhaust n' Ignite and get a kill.

Core itens:
Phantom Dancer
Berserker's Greaves
Trinity Force

You can take Bashee's Veil, Guardian Angel and Hexdrinker if you want.

Banshee's Veil if you is getting too mutch stuns, blinds, slows, etc...
Guardian Angel if enemy team is focusing too mutch at you...
and, at least, Hexdrinker if the enemy team has too mutch AP champions and your life is going too fast.

Well, how I said at the start, its my first build and feel free to comment it.
Sorry for bad english, it's because I'm brazilian.

See ya. (: