Hello this is Succ, I hit plat in season 10 primarily playing Mundo/Jax jg and thought I would share my builds :)

Jax has a solid clear from either buff, and is a very flexible champ. However, he is not a very good champ into CC heavy comps, as he is susceptible to it. Overall Jax is a great champ however for the chaos of solo Q. Who doesn't want a piece of the champ? :)

P-Relentless Assault
Jax's basic attacks on-attack grant him 3.5% − 11% (based on level) bonus attack speed for 2.5 seconds, stacking up to 8 times for a maximum of 28% − 88% (based on level) bonus attack speed.
Stacks are deducted one at a time every 0.25 seconds after not attacking for 2.5 seconds.
Q-Leap Strike
COST: 65 MANA
COOLDOWN: 8 / 7.5 / 7 / 6.5 / 6
ACTIVE: Jax Dash dashes to the target unit's location.
If his target is an enemy, he deals Attack damage physical damage to them.
PHYSICAL DAMAGE:
65 / 105 / 145 / 185 / 225 (+ 100% bonus AD) (+ 60% AP)
Jax will attempt to automatically basic attack his target at the end of the dash.
W-Empower
COST: 30 MANA
COOLDOWN: 7 / 6 / 5 / 4 / 3
ACTIVE: Jax's next basic attack on non-Turret icon structures or Leap Strike within 10 seconds deals Magic damage bonus magic damage. If Empower is used on a basic attack, it will have 50 bonus range.
MAGIC DAMAGE:
40 / 75 / 110 / 145 / 180 (+ 60% AP)
Empower resets Jax's basic attack timer.
Counter Strike
COST: 50 / 60 / 70 / 80 / 90 MANA
COOLDOWN: 14 / 12.5 / 11 / 9.5 / 8
ACTIVE: Jax enters Evasion, a defensive stance, for 2 seconds, causing all non-turret basic attacks against him to be dodged. Jax also takes 25% reduced damage from all champion area of effect abilities. Counter Strike can be recast after 1 second.
At the end of the duration, Jax stuns all nearby enemies for 1 second and deals physical damage to them, increased by 20% for each attack dodged, up to a 100% increase.
MINIMUM PHYSICAL DAMAGE:»
55 / 80 / 105 / 130 / 155 (+ 50% bonus AD)
RECAST: Jax ends Counter Strike early.
Grandmaster's Might
COST: 100 MANA
COOLDOWN: 80
PASSIVE: Jax's basic attacks on-hit grant a stack for 2.5 seconds. At 2 stacks, Jax's next basic attack on-hit deals bonus magic damage, consuming all stacks.
MAGIC DAMAGE:
100 / 140 / 180 (+ 70% AP)
ACTIVE: Jax gains bonus armor and magic resistance for 8 seconds.
BONUS ARMOR:
30 / 50 / 70 (+ 50% bonus AD)
BONUS MAGIC RESISTANCE:
30 / 50 / 70 (+ 20% AP)

Pros

Strong dmg
Auto reset with W
Good into AA based comps
R gives free dmg and Armor/MR

Cons
Can be hit by abilities
CC will ruin your game
Slightly weak early game

I like to go this item either first, second, or third. It just depends on if I am behind or not. If behind, I usually build 3rd.
Take this if you go straight tank, or are struggling with camp clears. Build this item 4th.
A solid item to build almost every game, take this item 5th.
Good item to take into AP heavy comps, if they can kite you easily. Also build if you have a healer support for more heals :). Build this item 5th or 6th.
Also a good item to take into heavy AP comps, especially long drawn out fights. Build this item 4th or 5th, depending on the state of the game.
A great item that gives you a phat shield, health, and some more damage! This is a good item to build into any sort of bursty team comp. Build this item 4th, 5th, or 6th.
Personally, I seldom use this. However in the right situation it can be a very good item. Build this item 6th and if you are 1v9 Jax Hypercarry.
I like this if I'm getting blown up while jumping in 1v5 :)

Try to get a bot side leash if possible.
If Red, Red-Raptors use -Wolves-Blue-Gromp-Scuttle
If Blue, Blue-Gromp-Wolves-Raptors use -Red-Scuttle

This is my second guide so I hope its helpful, thank you for reading this far! :) Be sure to comment if you have any questions/suggestions and please like the guide! My op.gg if you are curious https://na.op.gg/summoner/userName=G%C3%B8d%20Staff%20Jax