I will try to keep this short and sweet. This is my usual build while I play Tristana. It's an expensive and late gamer type build. So be warned that it's going to take a little while before you start to wreck havok.
PS: please don't take offense at my blunt sarcasm and humor
Being a glass cannon, you want to do as much damage as possible as quickly as possible. With that said, obvious rune choices to me are: Marks of armor penetration, Seals of attack speed, Glyphs of attack speed, and Quints of armor penetration.
You may be asking yourself: why the attack speed when I have a Q ability that gives me attack speed. The answer is this: YOUR SQUISHY! No two ways around it. Being slightly more meaty than an Ethiopian on a diet, you want to outgun your opponent and with the armor penetration at the start you can do this hopefully.
If I knew how to upload pictures of Trist's masteries and all that I would. Basically you want 21-0-9 getting as much damage as you can in offense, skip defense seeing as you are NOT a tank, and getting experience and gold for utility
This is what you came for. The build.
-Start with DORANS BLADE. Some extra life, damage, and life steal. Not bad to start with.
-Next you want speed. Franklin Roosevelt is faster than you and he had polio so you need speed. What's better than PHANTOM DANCER? Attack speed, movement and critical damage percentage. You can go a few different routes here. 1) work up the middle of the tree twice 2) work up middle of the tree once amd then go for a little damage 3) work up middle of the tree, then another dagger, then finish out phantom. This all depends on how you are doing. I like to get at least one phantom before i get anything else.
-Third item is either going to be BF SWORD. You can go one of two ways with it. INFINITY EDGE or BLOODTHIRSTER. Once again it will depend on what you need/want at the time. Either way, you need some bite you marshmellow.
-Fourth item: PHANTOM DANCER. Now you will at least have some ****py skates on your feet so you can get somewhere before the game is done. And depending on what you chose as your third item, you are going to be doing a critical hit 66 or 81% of the time. Can you say WOW. They won't know what hit them.
-Fifth item: BLOODTHRISTER. If you chose to get this as your third item, change it to INFINITY EDGE. You can now stay alive a little longer as well as do increased damage with any kill. So go get those pesky minions, ghosts, golems and all that. Become a money hungry banker.
-Sixth item: INFINITY EDGE or BLOODTHIRSTER you will now hit 100% critical or have a fair bit of lifesteal.
Be cautious, even with the amount of damage you are going to be doing and the lifesteal capabilities you now possess, THORN ARMOR WILL SCREW YOU OVER!!! and it will not, NOT give you a reach around or whisper sweet nothings while it bends you over
You can if you choose, change out a bloodthirster for black cleaver to damage those tanks
I don't know the skill breakdown per level, sorry. What I can tell you is that you want to start with EXPLOSIVE SHOT. Not only will it help kill minions faster but it is excellent at harassment and can get you a few champion kills if your opponent doesn't watch themselves.
Get a level is ROCKET JUMP the next two levels. Depending on how well your opponent is doing (assuming you took mid lane), it's up to you what to get. I max out rocket jump and explosive shot and get BUSTER SHOT when I can. I leave RAPID FIRE alone since you have a **** load of attack speed anyhow.
Call me noob, I don't care but I take HEAL and IGNITE. Heal because I'm made of glass or have you not been following along or no nothing about Trist. Ignite is always good to deal that extra damage. Name of the game is as much damage as possible as quickly as possible.
Trist is a glass cannon, so expect to die alot if you are going against anyone with thorn armor, or get ganked. You just won't have the hp, to last in the middle of a fight. Use your tanks as fodder while you pick the enemy off like a sniper.
Items: 2 phantom daggers
2 infinity edge
2 bloodthirster or 1 bloodthirster and 1 black cleaver
ultimate goal is to get 100 crit chance so you should be doing about 500-600 damage per shot