UPDATED! 4/11/11
THIS IS A 5V5 BUILD, FOR 3V3 USE A COMPLETELY DIFFERENT STRATEGY, THIS PROBABLY WON'T WORK

Hi welcome to my pseudo tank Jax build, you should probably have a real tank as the main tank, for example Shen or Rammas, but this build will beef you up so you won't die in half a second to casters, which are the only things that would be able to touch you.

Masteries

Very cookie-cutter, look at the build with the most rating for reasons why this one kicks ***.

Runes

From left to right in order of greatness.
Marks: Attack Speed/Armor Pen/Attack Dmg
Seals: Dodge/Flat Health/Attack Speed
Glyphs: Magic Resist/Attack Speed
Quintessences: Flat Health/Attack Speed

Summoner Skills

Exhaust: Can be used both offensive and defensively, useful early game for an escaping enemy before you get movement speed from Ninja Tabi and Phantom Dancer.

Cleanse: If you do well early game the best thing the enemy team can do is prevent you from getting fed. This ability, however, serves as the ultimate escape tool. With your points invested into Leap Strike you could leap onto your own unit while cleansing simultaneously for an easy slip. If you were getting ganked by physical targets, your 10% movement speed boost should be up making escape all the better.

Ghost: Ghost can serve as a great tool for both catching up to and escaping targets. While flash would be slightly better in most situations, ghost's position in the Utility tree make it too good to pass up.


Jax's Abilities

Equipment Mastery: Your passive, grants you health for ability power and even more for attack power. Equipment Mastery makes items like Guinsoo's, Atma's Impaler, and Bloodthirster so great.

Leap Strike: Great for catching and eluding, Leap Strike is the first skill you should max. Each point invested reduces the cooldown so you could spam it all you like. Early game, this skill serves as great harassment tool since it does not make enemy minions aggressive towards you (only use if enemy is in front of or alongside his creeps)

Empower: Minion-destroyer. When paired with Leap Strike, this skill can do decent damage. If this was before the Kog'maw patch, I would have suggested this be maxed before Counter Strike; however the cooldown time now does not change with points invested. Do not use Empower to kill creeps at an enemy tower when a hero is near, it will count as an attack and the tower will target you.

Counter Strike: This skill is why you should never focus fire Jax. With masteries, runes, and items contributing to dodge, this skill procs quite a lot. Use as your landing with Lamp Strike and Empower to deal incredible spike damage. Late Game, you should get minions to attack you so it is always procced get a stun on the enemy before they have the chance to react.

Relentless Assault]: Your primary nuke. Every consecutive auto attack increases your attack speed for a short period, and every third attack deals enormous magic damage. With good timing, you could jump an enemy with a combination of all your skills to deal obnoxiously high spike, ranged heroes beware...

Item Build

1.Ninja Tabi: This should always be your first goal. You should start with either Boots of Speed or Cloth Armor, and get one mana potion with the rest healing potions. Ninja Tabi grant you additional dodge: additional dodge= additional counter strike, whats not to love? Also movement speed increase is quite attractive.

2.Guinsoo's Rageblade: Another essential item. each successive attack gives you increased attack speed and damage. Goes nice with your passive and ultimate, which grant you more magic damage procs and health. To use this to its full potential, keep an eye on your stacks buff, then use a skill (Empower) as the buff is about to run out... this resets the timer and can give you the time you need to reach a nearby creep to keep your eight stacks up even longer.

3.Warmog's Armor Pure health... chances are you can destroy any physical in a fight, so Health would be good for survivability versus casters and tanks. It is good to build this early so you can start building stacks on it for more hp late game.

4.Frozen Mallet More health, and a slow... makes it easier to continue knocking your opponent silly while you build your Guinsoo stacks and your ultimate.

5.Atma's Impaler: Increases damage by a 2% of health. BUT WAIT! Doesn't your ultimate increase health by a portion of damage? Yep, so this badboy will cause your game health and damage to twitch for half a sec while it inputs a few formulas to calculate your final numbers. Most builds lack this item but I find it grants you much needed survivability.

6.Banshee's Veil: Chances are the only thing hurting you now are casters... really these sons of *****es are the only thing you should worry about in 5v5 games. After building this item you should be able to jump straight for any caster and prevent them from doing AoEs or heavy damage to your allies. Thanks to the rest of your items and passive, HP pool should be sitting at an astounding 5200 or so easily.

7.Force of Nature: The item that creates Gods, Force of Nature, will make you unstoppable. If the enemy chooses to ignore you, you will kill them. If they focus you, your team should kill them. This doesn't make you Rambo, but if the game is still 5v5 you will win.

x.Phantom Dancer or Bloodthirster: Depending on how your game is going, you are either engaging in plenty of ganks or pushing. If you are pushing, go for Bloodthirster, it grants health and lifesteal which allows you to be away from base for extremely long periods of time. If you are ganking, go for Phantom Dancers, these give lots of lovely stats, including dodge and movement speed, so that you can use your skills and ultimate even more, but this does not give much health, increasing the chances you will get killed within the duration of one stun.

Protips:
Only engage in battles you know you can win, especially early game. If a teammate is being overaggressive, tell him to get back. Chances are you won't get a proc on your Counter Strike when the enemy creeps are dead, and remember, you're worthless without either that or your ultimate.
LAST HIT EVERYTHING, even if it costs you an Empower or Lamp Strike.


Please comment with constructive criticism or experiences.