This is the Tristana build I have become accustomed to playing. This is a very skill-intensive build; I do NOT recommend it for people new to Tristana or even people who aren't incredibly comfortable with her. You may call it a glass cannon build if you wish, but it's guaranteed to get you lots of satisfying kills and "WTF" moments - like when you out-damage a Tryndamere in a point-blank brawl. :)

Note: This is primarily a ranked build. Chances are, people in a normal game will not be playing seriously enough to babysit you until you build up - this build is not for 20 minute pubstomp games. At all. Pick someone you trust to duo queue and tank for you, because you will need an effective tank to succeed with this build.

Pros:
Insane late game damage. Can easily pentakill an enemy team before they know what hit them. You crit for 800-1000 damage with over half of your autoattacks, at 2.5 autoattacks per second with your Q popped. You do the math.
Great mobility and escape abilities with W and Flash.
Great farmer with her AOE.

Cons:
Difficult to learn.
****ing difficult to master.
Incredibly squishy.
Incredibly item dependent.
Weak and team-dependent early and mid game.
Easily shut down in mid by AP nukers if you don't know what you're doing.

Conclusion: Easily the most rewarding character I have ever played, but also the most difficult and team reliant. Essential pick for a 5 man premade with reliable tanks.

Mostly self-explanatory here; I take ArPen marks and quints because it's too easy to stack armor and counter dps. Mana regen per 5 seals are just for laning longevity; Tristana is very conservative with her mana usage, you generally won't be using mana unless you're trying to kill someone or trying to get away from a fight. Cooldown glyphs are mainly for a shorter cooldown on your W - it *will* save your life.

More standard stuff here. There is some variety to be found in the offensive mastery tree, but I find that Tristana's range more than makes up for that 2% attack speed sacrifice. I take Greed in utility because this build is SO expensive and really hits its stride near the 45-50 minute mark; this gets you maximum utility from an otherwise not-too-useful mastery. A 45-minute game will get you about an extra 270 gold - enough for a few wards.

Make no mistake - this build is expensive. Your first item, IE, focuses on pure damage for easier farming and deadly pokes; your enemies will quickly learn that Tristana hurts like hell even without any attack speed. Immediately after that, you maximize the utility of IE's passive by building a Phantom Dancer. This gets you to about 55% crit chance at 250% crit damage - absolutely deadly in mid game. From there, a Black Cleaver helps counter armor so you can poke tanks with impunity as well.

At this point, you can go either Banshees if you're getting focused/nuked/CC'd, or straight to Madreds if you're really steamrolling that hard. I would always get a Banshees though for the longevity in teamfights.

Max your explosive shot first for maximum farming capability, then your W for maximum escape/gank capabilities. Q should be your last priority, since you can farm easily with your AOE damage without any additional attack speed.

I like Exhaust and Flash because they give you a bit of everything. Flash, combined with W, gives you incredible GTFO mobility for escaping a bad situation, and Exhaust lets you win one-on-one brawls if worse comes to worst. These two spells, in my opinion, can be used very creatively to escape ganks or even to outmaneuver an enemy for an awesome kill.

The key to this build is FARM.

Let me repeat myself.

FARM.

Tristana is completely item dependent - if she doesn't have good items, she is useless in a teamfight. You should ALWAYS take mid, and ALWAYS focus on farming. If you miss more than 1-2 last hits per minion wave, you are failing and should quit. Even only missing 1-2 last hits per wave, it will still take you 45 minutes and a lot of jungling in order to build up.

Oh, speaking of jungling - if your jungler doesn't mind, or if you don't have a jungler, hop over (literally, W) to your wraiths every time they're up and grab a quick gold and XP boost. They add up substantially through the game.

(To be added)