So this is my personal build for Tryndamere. I recommend it because it gives you 83% crit chance, and you really don't need more, because your passive gives you the rest in team fight, and you wont ever not crit before you're down to 80% health, and 100% crit chance.
Important note, is that can go through walls. This allows you to use a 'flashlike' ability every few seconds.

In lack of better, use any offensive runes. But you should always aim for crit. I recommend this:
9x
9x
9x [ocon=Greater seal of furor]

3x

To sum up: Lot's of extra crit dmg. If you want you can also replace the glyphs with some crit dmg.

Masteries are 22-8-0. Offense and defense. Bucketloads of dmg, and you wont be able to die.

Open with brawler's greaves and two healing potions. When you got 350 gold, go back and buy averice blade. This is just for now. Next you buy and quickly build it into [infinity edge]. If you want, grab some before infinity edge. At this point, you can kill anything. Next you go for Normally you should go for the crit first, but in this chase, take the lifesteal. Next is . Then you buy a and you end with a

It goes like this: e-q-q-w-q-r-q-w-q-w-r-w-w-e-e-r-e-e. Take the at first because it allows you to escape almost anything. As good as flash. BUT! it costs 40 health, so don't use it when you're too low. 41 hp and above is ok. Then try to lasthit minions, and attack as much as possible to gain stacks from .

and . These are the best two summoner spells. No reason not to take advantage of that fact.

So in short, tryndamere is a beast. From level 1, he deals incredible damage. And at level 6, you can't kill him either. A good tryndamere can win ANY game.

Try to stay in the fight for as long as possible, but don't be afraid to open the teamfight with a because it decreases attack damage. Others will follow you. Just be careful if you're against champs with heavy stun. If you are, you should let the tank in first, or start with your ultimate. When at 1 hp with your ultimate, run towards a nearby wall, use over the wall, and use . You will instantly be at 400 health. Watch how the fight goes. If you think you can survive it, return to the teamfight. If you can't, rush to the nearest jungle camp and kill them. Use whenever you're at 8 stacks. Also try to be at eight stacks if possible when you enter a teamfight, because it gives you MASSIVE damage boost for your critical strikes.

Pros: You're almost impossible to kill.
You do MASSIVE damage.
You crit 99% of the time for 1k damage.
You can escape almost every situation.
You can decrease enemy's attack damage in aoe with 100.
You get amazing laning power from
You can solo dragon and red buff at lvl 7 with no problems.
You can tank baron.

Cons: You're easy to counter with either ability power, or stuns. Make sure to avoid being stunlocked.
You're not too tanky. Your ultimate and frozen mallet makes up for this.
However, you will be focused because people want you to use your ultimate so that they can kill you at the end of the teamfight.

Not much to say. In early levels you can 2 or 3shot minions with crits. At level 18 you can onehit all regular minions. Make sure to do this, to stack up to heal, and do extra damage.