What's up all! This is my first guide so please be nice, vote and comment accordingly if you wish :)
I've only been playing league of Legends for about 2 months now and I quickly grasped the concept from playing DOTA on Warcraft 3. I tend to favor carries more than tanking champs but I'll also play some support now and then and I'll post the builds I use soon enough. AD and AP carries are what I more specialize in and if need be build them as hybrids.

Attack Damage - AD
Ability Power - AP
Armor Penetration - ArP
Attack Speed - AS
Magic Penetration Rune- MrP

This has been my build I found that worked for me in almost every game that I tend to play tryndamere in. I like the extra attack speed because I max out on critical strike to begin with late game. If more than one or two of their champs happen to get thornmail, I switch the boots for Warmog's armor so he becomes a little more of a hybrid. Any questions or comments feel free to ask.

Tryndamere is an escape artist and is just one of those champs that if built correctly and played well, will piss most people off and make them focus more on getting items to counter you or at least slow you down. Thornmail for instance, only really works if its put on tanks or tankish champs :) I've seen people put it on Miss Fortune, Eve, and other squishy champs to try and make them non squishy and make them last longer. Well for you this is a good thing because you when critical striking them for a fourth or third of their health, thornmail doesn't do much and is a waste of gold for them which means you last longer. Tanks are the only problem and as tryndamere, in my opinion you should be the last to enter the fight but from the side or behind and take care of the squishy champs first before going after the tank so that way the tank is just there alone.

This is one part makes the biggest difference in the beginning. regaining health is crucial and being able to consume your bloodlust stacks to regain health is one of the best spells for tryndamere. After that mocking shout or spinning slash is up to you. I personally go for spinning slash, but i've seen others go for mocking shout first which is more reasonable to slow them down more to catch up more quickly. Timing your Endless rage is crucial to everything when doing 1v1 1v2 or more and team fights. when you are focused in team fights, being in endless rage gives your allies at least another 2-3 seconds to be able to tear the other team apart and then you can spin out and use your bloodlust stacks to heal and easily escape

ArP- Early game has a huge boost in the damage dealt seeing as critical strikes come less frequent even if I was to be runed for it.
AS- even though people consider attack speed in the lower tier of runes I find it to be more important cause it can make all the difference in the beginning and later in the game.
AS- Again the same deal with the Sealsand for that I stack them still
ArP- You can honestly never have enough ArP with Trydamere. Enough said.

For this I do a flat 21/0/9 for masteries. the 5% extra experience and 4% extra health regen makes a huge difference early game and can give you an edge on other champs early game

Pros

Very versatile and attack quick in the beginning and throughout the rest of the game for quick kills on the "Squishy" champs.
Able to jungle easily early or late game. Also able to solo baron once build is complete.

Cons

May be easy to counter early game and can cause you to be focused.
very costly and sometimes demands kills if you dont get any minion kills

As for Kennen, I've found him to be kinda vulnerable in every aspect regardless of how good or bad the other team is. Whether the fact is you get Mejai's or just mass Ability Power, both get you targeted not to mention kennen's skills as well. Ryjai's scepter is a must after you get boots of swiftness.

Runes- for the seals i use the energy regen per level, (Seal of greater ludicity). They did not have the seal to select from so this is where I had to include it.

Magic Penetration Runes- Works great with Kennen seeing as he is a ability power monster. Ignoring most of their Magic Resistance amplifies the amount of damage you can deliver
Energy Regen per Level- or Seal of greater Lucidity will help you recover your energy much quicker to keep dishing out more damage
AP per lvl- gaining more AP as you level in the beginning instead of straight AP will help more because you will in turn gain +2 more AP for each rune by the time your level 18
AP- +5 AP right from the start per rune can me all the difference in trying to get that first blood or regardless of just trying to kill the enemy

I do a flat 9/21/0. I've felt that kennen benefits more from the defensive tree due to the fact the 4% decreased physical and magic damage reduced and also the extra 4% ability power I think scales as you get more AP.