Hello and welcome to my Irelia bulid so dont be to rough i tryed my best ^^

Pros
+ Great burst
+ Good mix of Magic, Physical and Pure damage makes you hard to counter.
+ Mana effective
+ Flexible (Great assasin early game, good burster mid game, great dpser late game)
+ Quite team undependant
+ Good health regen even without lifesteal
+ Great farmer
+ Not that vurneable to CC due to passive
+ Good melee dps that can deal damage even when blinded
+ Thornmail will not hurt you that much :)
+ Good CC

Cons
- Squishy mid game
- Cooldown dependant
- Cant focus on 1 thing makes itemisation hard
- Dependable on kills/killsteals
- Costy itemisation

Im using 21/9/0 so in defence so in Defence i take NIMBLENESS and i take Criple for my exhaust spell

On lvl 1 i take Bladesurge so i have a good farming and jumping tool and i max it as soon as i cant if i cant take Bladesurge,i take Equlibrium Strike and max it after Bladesurge.Also take
hITEN sTYLE so you get a nice life steal on attack+nice dmg wehn act.
In Early game your combo will be Bladesurge/equlibrium strike.
In Mid game start with Bladesurge/Hiten Style/Equlibrium strike and attack constantly with Transcendent Blades.Becose of Irelia's passive she is very good in team fights or in escapeing
becose if an enemy champion is near her CC's are reduced

For summoner spells i take Flash/Exhaust.
FLASH:Rly good tracing/escaping spell this spell saved me alot of times
Exhaust:rly good for runing and killing some1

I use Armor pene/dodge/cd/quint armor pene

For farming just LH minions and you can kill them with Bladesurge it will refresh some of your mana and cd

I start with Dorans Blade and rush for mercury treads.Mercury with your passive is rly great expecily in ranked games.Then i go for Wits end it gives magic ressist and attack speed with good passive to burn mana.After that i go trinity,then Banshes(spell block and and magic resist/hp/mana)then go for guardiran or thornmail your choise and then bloodthirster/black cleaver/Ie depends.