This build is not for the feint of heart. This is the build that I use with my favorite champion Tristana. After much toying and tinkering, this is what I came up with. I do not deny that I take a lot of flack in games from people talking about me taking vampiric scepter first, or stacking two of them to start the game. This is an expensive, late game build. It starts slow, but allows you to stay in lane and farm for a long time, without having to go back to base even when your health gets low. Dont knock this build until you try it, and get the full build. Once you have reached the full build, you will see how insane your damage output is. This build allows you to solo baron with only a partial build, and you can kill any champion with just a few hits, even if they have thornmail.

Pros:
Fast attack speed
Extremely high damage output
Consistent damage, not burst
High amount of life steal'

Cons:
Squishy
Vulnerable to crowd control

For runes, I go with armor penetration marks and quints, and attack speed seals and glyphs. The armor pen helps a ton with damage, especially early game where you aren't buying your damage items yet. The attack speed is self explanatory.

I go 21-1-8 with my masteries, putting one point into heal. I know, only noobs use heal. I can't tell you how many times heal has gotten me a kill though. Early game, you are low health, and a champ moves in for the kill on you. simply rocket jump, hit d, e, and finish them off. You would be surprised at how often it scores the kill. Heal also lets you survive early gank attempts or if you make a mistake in lane.
Lets face it, what else are you going to use? Ignite is a bad idea, her e is ignite, she doesn't need ghost, cripple, or flash because of rocket jump, simply put, heal pulls your butt, and your teammates' butts out of the fire all too often not to take it with her.

Okay, as I mentioned above, I take heal. I defend my point above, feed free to disagree. I also take teleport. I take it for a few reasons. First, it allows your to get back to lane very quickly after going back to base to buy. if you kill the other champ in lane, you can go back, buy, heal, and teleport back before they get back to lane. Big advantage to you. Second, when you are filling your bloodthirsters, if you see a big group of minions somewhere on the map, drop in on them and pick up a quick easy 20 minion kills and 500 or so gold. Third, it helps you defend your turrets, if I need to explain that, you need to go play a different game. Last, there are opportunities late game to back door, and there are plenty of times where I've been able to teleport in, take out an inhib turret and and inhib, and sometimes even a nexus turret, before the opposing team could respond. This is also a great way to get them away from your base when they are trying to push you. (the reverse pac man)

Most builds emphasize rapid fire. Rapid fire is an awesome skill for taking out enemies and turrets. I however, emphasize building explosive shot as quickly as possible. It helps you tremendously early game with harassment. I will explain this later on.
First grab explosive shot, so you have your harass, then grab one rank in rocket jump. You only use your rocket jump to escape, or close the gap on the enemy, you do not need it for damage. The distance you jump doesn't change with level, so its pointless to put points in it early. So only put 1 point into rocket jump at level 2, then don't touch it until you have to. The reason you don't put more points into rapid fire early is that you don't use it much. You usually don't get into a heads up fire fight with an opponent early, so you don't need it there, and I don't emphasize pushing turrets hard early, so again, explosive shot is the key.

Here we go. How about a little more controversy. I hope by now you noticed that the build has no boots. No boots? I really must be a noob. Hear me out before you pass judgment.
Rocket jump lets you move a fair distance. Buster shot throws the enemy back quite a bit. These two skills let you get away pretty effectively. The extra run speed from boots is nice, but isn't needed. Two phantom dancers are almost just as fast as boots, and with this build, you rarely run.
Start out with a vampiric scepter. I know, no doran's blade? No. The life steal from the scepter allows you to stay in lane longer. You aren't going to sit and trade blows with another champion, at least not right away. You want to land your explosive shot, and move back. So the scepter allows you to heal up the damage you took landing explosive. I will explain more on this later.
Here is what you want to get.
2 vampiric scepters, then build a phantom dancer, then a blood thirster, then a phantom dancer, then 2 blood thirsters, then infinity edge.
Why this combination of items? Well the phantom dancers give you the run speed of boots, along with awesome attack speed and crit chance. infinity edge gives you damage, crit chacne, and makes your crits do more damage. then blood thirsters give you a ton of damage and life steal.
In all, you end up with 85% crit chance from just your items, so nearly every hit is a crit, and you hit for over 1300 damage, along with 75% life steal. Thats an insane amount of SUSTAINED damage. And the life steal means that if you get low, you just back off and heal off of minions or monsters, and go back into the fight. This also means you dont depend on mana at all.

Take mid. More importantly.... take mid. Then, TAKE MID. Get it? TAKE MID.
Of course, attack minions, get the last shot on them, get money, blah blah.
Usually you want to keep behind your minions like a shield, at least until you can gain an advantage over your opponent. Most people will try to get close enough to you to hit you, but stay out of your auto attack range, which sucks early game. When they move into you, move into them, hit them with explosive shot and 1 auto attack, then move back. get to max distance from an enemy minion, and attack them to heal up. Most people don't use vampiric scepter, so they will sit and burn health pots to heal. Try to land an explosive shot on them while they are healing up, it will cut the healing by half for the 5 second duration of explosive shot.
Keep your rocket jump on standby. Too many noob tristanas use their rocket jump on minions. Don't do it. Keep your rocket jump for escaping from ganks, or to score quick kills.
Work your enemy down to low health, and heal yourself up, they will try to hang back by their turret. This is what you want. When they get low enough to where your explosive shot can kill them. get 250 or so mana together, rocket jump next to them, hit them with your explosive shot, and attack them, when they die, rocket jump back out, or hit them with rocket jump, then run away out of turret range. When you score a kill or assist, rocket jump auto refreshes, so no CD when you score a kill. Turret dive away! If after level 6, this is even easier, rocket jump, explosive shot, buster shot, rocket jump out. If you can get them close to your tower, you can rocket jump behind them, and buster shot them into your turret, they will take a ton of damage, and will be slowed, giving the turret a bunch of free shots on them, while you shoot them as well.
I wait until I have my first blood thirster before I seriously push their first turret. I like to keep a short lane between me and my turret, so I can jump back for safety if I get ganked.
After their first mid turret goes down, Time to move to mid/late game strategy.

I lump these two together for a reason. To me, with tristana, they are pretty much the same thing. After the first mid turret drops, it's game on. At this point you should have built at least one blood thirster and one phantom dancer. Your goal is to get that blood thirster as fed as you can. Take every opportunity to kill minions and neutral monsters. Move to where your team is, but try to take a side route so you can flank the enemy team.
When your team engages, you can rocket jump behind someone, and buster shot them into your team to help single a target out. If you can rocket jump right next to them, they will be slowed when they go flying into your teammates, and should be dead before they know what hit them. Try to catch fleeing enemies with your rocket jump, and if they have a little health, try to combo that off with explosive shot or buster shot. I get many kills this way, rocket jumping barely into range to land a skill to kill them.
Work on completing your build.
If you get an enemy or two dead, don't be afraid to go rogue, away from your group to push a separate lane, if they have to divide their attention, that's better for the team. Just be cautious and watch for the gank. Often times you can take a turret down just as quick as the rest of your group combined, so you will pull a lot of attention from the rest of your group.
After you get 2 phantom dancers, and 2 blood thirsters, and you get 40 minion kills on the blood thirsters, you should be able to solo baron. Those that arent used to it, might want to get the third blood thirster, or at least a bf sword to attempt it. All you do is run up, and auto attack him. If you have your build rockin, you should be able to life steal more than the damage he is doing to you simply by auto attacking. If for some reason he is doing a little more than you can handle, pop your rapid fire and your health bar should fill right up.
I get "trist can't solo baron" all the time, but when I can grab him while my team pushes a turret, they are all thankful.
Before too long, you WILL be THE target for the other team. They will go out of their way to kill you. They will turret dive, and run past several of your teammates, and sacrifice 2 or 3 champions to kill you. Use this to your advantage. Hang back more, make them work harder to get to you. at level 18 you have the longest range in the game, so you don't have to get close to anyone. Take a pot shot here and there.
If the other team pushes to one of your towers, just sit back by the tower and harass them. You, and they, will be surprised by how much damage one of your auto attacks will do. Just harass them long enough for one of them to make a mistake.
Once you have your full build, nearly every hit will br a crit, and they will be for over 1300 damage, before armor modifiers. Even tanks like rammus, with thornmail, will die very quickly once you start attacking them. Squishies, like veigar, will die in about 3 hits. You can walk up to baron and solo him with just your auto attack.

Tristana is a powerful champ. You would be hard pressed to find a champ that can lay down the kind of sustained damage tristana can with this build. It seems very counter intuitive, but it works, and works really well.
Thanks for taking a look at my very first published build. I know once you actually try it, you will love it!