Not Updated For Current Season
My build is a build which works very well there 5c5 but also 3c3
1st step: Items
Take, Executioner's Calling, Mallady, Last Whisper, The Bloodthirster, The Black Cleaver and Infinity Edge.
-> It may looks very expensive but you can buy all of them in 5vs5, the most important item that you should absolutly have is the Infinity Edge. After buying that, killing ennemies is easy with your ultimate.
If you have too much money, you can replace the first 2 items by 2 bloodthirstiness. And if after that the part(party) does not still end, think has to take 4 elexires!
2nd step: Skills
1 - Bloodlust
2 - Mocking Shout
3 - Spinning Slash
-> Take 1 until you reach the maximum, when you can't, take 2. The third skill isn't that usefull, it may make some damages but Bloodlust allows you to make more critical hits, which allows you to make more damages compared to the damages you'll make with Spinning Slash.
3rd step: Runes
Armor penetration and the most important : more damages when critical hits. I didn't take attack speed runes because speed is not the most important thing with Tryndamere.
4st step: Mastery Trees
I take 21-0-9 because Tryndamere must have low hp to make critical hits so spending points on Defense is completely useless.