the reason i build so tanky is because trinity force gives you enough damage because of the true damage gained from w, frozen heart really helps you out duel people like fiora who are attack speed/ basic attack reliant. the sunfires cape offers you good damage as well since you will always be with its range when fighting, I like swiftness boots on her because it helps you stay in range of your e and basic attacks, visage is also good on her because of her w and ult plus it gives nice cooldowns same with frozen heart, and ga because its gives good mr and armour and ofcourse brings you back to life

I pretty much always go with tp and flash she really needs flash as she can be quiet prone to ganks and it also helps you catch up with targets that are out of reach of q, I bring tp because you'll be doing a lot of split pushing with her and it helps you get to team fights while doing so or helping with dragon and such. you can bring ignite if you against a laner like volibear or mundo just so there heals arent to much but its not necessary

pros-

really good mid game
good roamer/ assassin
good duelist
good split pusher
has a really nice ult thats easy to use and hit plus is on a low cd

cons-
gets bullied by a few champs
has trouble in the late game
can be targeted easy in team fights

irelia needs farm, which is really easy to do on her, if you are going to miss a minion with basic attack just q it will reset on a kill of any kind be it minion, champing or jungle camp

When comboing start with e then w then r get as mean hits as you can in before using q unless your using to secure then, then just keep goign through the rotation or e w