With that guide you can make a Tristana that can kill any char, even thanks with thornmail or something like that.
And the best part is that you can x1 any of the other team character. Any.

   1º Tristana - The usual build.
   2º Tristana - Life Steal build. (Surpass Thornmail)
   3º Tristana - Ultimate Tristana. (Take some time and gold)
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I like to use the teleport to destroy turrents and come back to the lane faster. You can switch to any other thing you want.

About the itens... you must have the Infinity Edge, Phantom Dancer and Last Whisper. The other itens I like to use because the attack speed / life steal / move speed.
I already made a build that had: Infinity Edge, Last Whisper, Phantom Dancer, two Trinity Force (Triforce) and the Hextech Gunblade. It kicked some ***es really nice.
Another build to surpass the thornmail is to make the Hextech Gunblade with a Stark's Fervor because you'll have 40% life steal and will take 30% damage, witch make you have a 10% life steal. At least you won't die that easily.

You can change de sequence to rise the Rapid Fire to destroy turrents easier. It's up to you.
And make sure that when possible, use the Explosive Shot (especially at the beginning of the game) to mess the other team up. That skill is like an igite, but do more damage and you can use more often.