It is build based on "Maximum Glass Cannon Tristana [1.0.0.110]" with some changes.

9x

Greater Mark of Desolation

- Does more DPS than crit dmg runes, especially in early-game.

9x

Greater Seal of Malice

- Gives you that little extra crit chance you need in early-game.

9x

Greater Glyph of Furor

- You need to inc your crit dmg(+Infinity Edge + Rapid Fire = enormous dmg)

3x

Greater Quintessence of Desolation

- Must-have for Armor Penetration, the single stat that you're lacking most with this build (but it's still worth it).

Standing 21/0/9 build, there's really no other way to build her. You don't spam skillshots unlike Ashe or Sivir so no need for the 21 utility points.

Important Masteries:

Havoc

- Must-have

Lethality

- Also a must-have, crit builds are simply the dominant damage dealing builds available

Archaic Knowledge

- Do not underestimate the power of 15% spell penetration on Buster Shot or Explosive Shot

Deadliness

- You *need* crit chance in early and mid game

Avoid the following:

Offensive Mastery

- Completely useless. Last-hitting isn't a problem even without the 4 extra damage to creeps.

Ignite

- Very good offensive pick, great for first blood, good for finishing runners (for example Tryndamere), and excellent against healers. I personally get this because I like strong early game presence, but it's rather useless for late-game as you already have Explosive Shot to counter healing. Still, if getting kills early on wins you the game, it's a solid choice. Ignite + Buster Shot will finish off everybody under ~30% HP.

Exhaust

- A very good spell, both offensive and defensive. After the change which allows it to reduce the damage of spellcasters it's practically a must-have for every single team. Combine it with the slow you already have to make it impossible for an enemy to get away even if they have flash. Also, the 10 reduced armor with Cripple make a significant difference in first blood scenarios.

Flash

- It is much better from Ghost (since 1.30.17) You can use it when you have CD on Rocket Jump. Very useful for First Blood.

Cleanse

- Great to break out of CC prematurely so you can Rocket Jump away. A real life-saver.

The first two are offensive, last is defensive. Flash you can use as offesive and to run away. Mix and match them according to your playstyle. I personally roll with Ignite + Exhaust but any combination of the above are excellent picks.

Bad choices

Ghost

Since 1.30.17 it is useless.

Fortify, Clairvoyance, Rally

- Leave these for your supporters.

Clarity

- You won't have mana problems with runes.

Revive, Smite

- Simply useless.

Starting Items

Doran's Blade

or

Doran's Shield

- Get the blade if you're facing a squishy and want to deal more damage, get first blood, etc.
- Get the shield if you need more HP regeneration, for example if you're facing somebody who can harass well.

First trip back

You shouldn't need to go back at all until you have over 1850 gold. Once you do, go back and purchase a

B. F. Sword

. If you do have to go back sooner, or if you're facing somebody like Karthus who can spam skillshots, you can get a

Pickaxe

+

Boots of Speeg

instead.

It is important to note that you build your sword you will be doing a ton of damage. You can start playing aggressively, enemy squishies should drop in no more than ~3 auto-attacks + your spell combo. I usually try to "surprise" my enemies by playing passively until I get the sword, then jumping at them with unexpected damage.

Second trip back

If you started with a sword, pick up the Pickaxe + Boots of Speed now. If you started with the Pickaxe, pick up the missing B. F. Sword.

Third trip back

Finish your Infinity Edge. This will be the most significant damage boost you will ever experience throughout the game.

Mid-game

Mercury's Treads

- Pick these up after your infinity edge, try not to get them before you do as you are ridiculously item dependent and unlike other champions, boots alone will not allow you to kill people.

1.

Infinity Edge + The Black Cleaver

- A simply awesome combination. The armor pen and attack speed on the cleaver plus the raw damage of the edge will obliterate any squishy enemy in several hits at this point. A single crit should be taking away like 30% of an enemy's life. (Note: I used to have a Sword of the Divine here, but TBC is better even though it costs 1k more - it still outperforms a SotD + Zeal)

2a.

Banshee's Veil

or

Frozen Heart

It helps you to survive in huge fights.

Late-game

1.

Frozen Mallet

This item inc. your hp by 700. Request: You are almoust Immortal.

2.

The Bloodthirster

- The only thing you need to top off the build now is more damage and life-steal, which can both be obtained from bloodthirsters. If possible, you can even purchase a second one as sixth item, rendering your build complete. If you need more survivability, start with Vampiric Scepter. If you need more raw damage, start with B. F. Sword.

Elixir of Fortitude + Elixir of Agility

- Get these whenever you can after finishing your first Zeal. They provide a nice but small boost. Any sooner will only unnecessarily delay your core build.

Items to avoid

Vampiric Scepter

- This is *NOT* a good start item, despite what many builds tell you. Lifesteal is the only stat you *don't* need at the beginning. You need damage to get last hits and first blood, and health to survive enemy combos/ganks. Doran's Blade provides you with both of this. Lifesteal won't do anything unless you're auto-attacking creeps all the time, which is a very bad thing to do. Plus, a Doran's Shield will provide you with more health regeneration than a scepter will let you heal.

Long Sword

- Some characters need this to trigger passives. You don't. The 2 AD don't make a difference.

Doran's Blade stacking

- Stacking them is a waste of money once mid-game starts. Sure, you have a lot of extra health and a very efficient way to get AD per money, but the AD that it provides is still completely insignificant compared to the AD you could be getting for the same money by building towards your Infinity Edge.

Phantom Dancer

- It is useless because Tristana has Rapid fire.

Youmuu's Ghostblade

- Even with the active, it won't deal as much damage as a Phantom Dancer.

Malady

- A terrible item before the change, a terrible item after the change. *Never* get it.

Sword of the Divine

Black Cleaver outperforms it after the 1.0.0.108 patch:

I haven't made the graphs pretty, but here's the information for those curious (numbers listed in DPS, first two are at level 18 with a full item build, the second two is at level 11 with just IE + one item, I added a Zeal to the SotD build to make up for the missing 1k gold)

SoTD:
vs squishy: 1687
vs nonsquishy: 1328
vs tank: 495

TBC:
vs squishy: 1836
vs nonsquishy: 1419
vs tank: 504

SotD:
vs squishy: 439
vs nonsquishy: 348
vs tank: 133

TBC:
vs squishy: 506
vs nonsquishy: 393
vs tank: 141

Situational items

Last Whisper

- Ever since the nerf on this item it is no longer as important for Tristana. Sure, you can deal a bit more damage to armor-stacking tanks, but they usually have Thornmail so doing lots of damage to them isn't as important in the first place.

Madred's Bloodrazor

- Only get this if you absolutely need it (for example with Olaf, Cho-Gath, Mordekaiser or Vladimir in the enemy team stacking nothing but health with hardly any resistances). I still don't think it's the AD carry's job to get this item though, leave it to somebody else. You could experiment with replacing a Sword of the Divine by it, but you won't deal enough damage without the armor penetration on its active.