I saw the words tanks will kill you and stopped reading. If you got killed by a tank there's no other way to say it. You were out of position. "Kill you before you get there" what makes you think anyone in the right mind will walk right through a team fight? There was also no reason whatsoever to prompt any rudeness in your response, but now that you have I have no obligation to be polite. To put it in your own words "Well I don't know what elo you are playing in, but you would die in 3 seconds with your build. You aren't going to walk through the whole enemy team and survive just because you bought a banshee's veil".

And I'll be honest with you, I am not level 30. I have never played a ranked game. However I do frequently play with my 1800-1900 elo friends and yes I have used this build successfully.

Well I don't know what elo you are playing in, but you would die in 2 seconds with this build. You aren't going to hit their squishies cuz their tanks will kill you before you get there.

Last whisper is unnecessary unless the enemy team is stacking armor. If you use it on a squishy, who has say 90 armor, you only shred 36 armor. That would only increase your damage by about 12%. The extra 60 AD from another bloodthister will easily make up for that damage difference. And of course vs a tanky team I already suggested getting LW.

As for the Banshee's veil the same concept applies. If you have 30 magic res you take 100/(100+30-20) = 10% reduction (20 pen from sorcs shoes). Now if you had a banshee's veil then that would become:
100/(100+30+50-20) = 37.5% reduction. This seems like a lot more at first, but lets consider say Annie's burst. If she has 500 AP endgame she'll do (595 + 655 + 800) * .9 = 1845 without Banshee's veil. With banshees: (595 + 655 + 800) * .625 = 1281. You reduced 564 damage, but 1281 damage is still way more than enough to put you at low enough health to be finished in 1 more hit. If the caster was Annie then after her burst is done you are probably still stunned for another .75 seconds. All it takes is one more hit from one of her teammates to finish you. And the bubble is so easily popped. The enemy Ashe can just fire a volley at your team and pop all of the veils in 1 go. Maybe if the veil had a minimum damage before being consumed then it would be more viable, but as of right now it breaks no matter how little damage you receive.

And if you drop a BT then you also lose 25% lifesteal, which arguably is your defense since you steal so much life back.

I think you need some more defensive items and some armor penetration. Try subbing a BV for a pd and a last whisper for a BT.