jax is a melee hybrid i will show my build for him critism is allowed as this is my first build and it may not be for everyone

for seals i get Greater Seal of Evasion for marks Greater Mark of Attack Speed because i like attack speed over damage on jax. for glyphs i go with Greater Glyph of Cooldown Reduction so you can spam that stun!

i go with a standard 21/9/0 taking all the dodge and taking all the brutal force

i focus all skills about the but i tend to max counter strike before leap strike and then emp power

i go with Cleanse and Exhaust but other good choices are

Ignite Flash Ghost

first i go for either Dorans Ring or Regrowth Pendant followed by Ninja Tabi now you can pick which you want first it can be Hextech Gunblade or Frozen Mallet but you must get both of them the last item is your choice depending on how the game is going

once you have started the gunblade or the mallet you can start using your amazing gank power but remember after the gank get back in lane and forget about ganking for a while cause this may be a good build but it aint cheap

remember please be a critic cause this is my first guide :)