You build Ghostblade for the active. If you feel you need an attack speed increase and move speed increase, then you go Ghostblade. Otherwise, you get a Brutalizer and stop. Many tanky DPS champs will get an early Brutalizer and sell it late game for better items.
If you are melting as Irelia, then you probably didn't build her tanky enough. What is your build?
As for my build, I start with regrowth pendant. I used to build this into philo stone, and this gave me good results, but should I save this for Warmog's? I then get heart of gold and boots on next back, or mercury treads if I've been doing well and so have enough gold. I'll probably build Warmog's (assuming I kept that pendant) here. I start going situationally here. If they have a LOT of magic damage I'll get Negatron asap here then build Force of Nature. Otherwise, I'll get Chain Vest then I'll probably build Atma's, since the armor and damage are great. Regardless I like to finish my Randuin's Omen from that Heart of gold somewhere here. If I think that I'm doing alright I like to buy Brutalizer here. Then I'll look again. If they have a Yi or Trynd (or another dps, depending) doing well I'll get Thornmail. If they have Magic dealers who are doing decently, or one that is doing well, I'll still probably get FoN since I find the movement to be extremely useful. I think I'll probably buy Ghostblade here to finish.