If you are looking for a champ that will always be fun to play Lee Sin is what you are looking for, this is more of a AD build with some optional tanky items/routes to build in it

Pros:
His skill shot is amazingly fun
Amazing burst with Q
Very hard to Catch/kill
Tanky/can save other peoples lives
very good team fight ultimate
ultimate can interrupt thinks like katarina's ult and what not
Cons:
Ganking can be hard if you don't land Q
Very easy to misjudge the range on your cripple, your E
Can be squishy early on
If he can't safeguard out(W) it is hard to survive

Runes are as shown at the top although, if you want fortitude quints go for it it may help early game.

as my masteries i use a stander 21/0/9 jungle set up.

i love the 10% reduced death timer but you may prefer the regeneration in utility, personal preference really.

This build is mainly for AD and dealing damage. if you are looking for a more tanky build i would suggest going into a standard tanky jungle build

ITEMS!
CORE:
Vampiric Scepter
i start of with vampric scepter, helps very much in the juggling face, i prefer this over other juggling starting items because u don't lose any gold,like when u buy armor and 5 pots.
Wriggle's Lantern
A must for lee sin jungle. once u have this item juggling becomes 100x easier, not to mention the free ward, usually placed next to dragon. the life steal and damage really help you as well
Phage
Very good early game item on Lee Sin, gives you a enough damage to do some good burst while giving you enough health to survive early game.
Atmas Impaler
some people wonder why i get this item next, well getting this item after phage gives you about 40 extra damage a hit not to mention the extra armor and crit!! also the crit is amazing and the armor is amazing for surviving that extra 10 seconds!

OPTIONAL paths after core build

if you are doing well early game and want to wreck some more face you can go Trinity Force / Bloodthirster / Warmog's Armor / Bloodthirster

if you think you need to go a bit more tanky you may want to go with Warmog's Armor / Trinity Force / Force of Nature / Bloodthirster

Optional items:

Hexdrinker : very useful mid and early game against fed ap champs

Infinity Edge : With Trinity force and Atmas you will be critting a decent amount of the time, this item is not a bad choice.

Last Whisper : if the other team has just too much armor!

Skill sequence:
Prioritize: Dragon's Rage > Sonic Wave / Resonating Strike > Safeguard / Iron Will > Tempest / Cripple , some prefer to get 2-3 points in Safeguard / Iron Will early, if you prefer the extra life steal and what not, go for it

I honestly only recommend Flash and Smite ...and possible Ghost if you are a pro at getting away with q/w
You don't need exhaust because you have a built in exhaust(cripple) and all the other spells are useless on lee aswell

JUNGLING!!!!!
DO NOT FORGET: Keep in mind, always use your E immediately AFTER an auto attack. and UTILIZE YOUR PASSIVE Flurry . example of what you should be doing, auto attack->E->auto attack->auto attack->E again->auto attack-> auto attack.

My route:
Start with Wolves, killing the big one first,Keep in mind, always use your E immediately AFTER an auto attack. and UTILIZE YOUR PASSIVE. example of what you should be doing, auto attack->E->auto attack->auto attack->E again->auto attack-> auto attack.

Then go to the wraiths, you want to smite the big blue wraith at max range, getting and using your W before the small ones can hit you and still using your passive!

AFter you clear them go to the double golem camp, just spam W and E and use your passive correctly, you may get low on health but its ok.

Grab Q and Go back after golems, get armor and 1-2 health pots

Wolves again,(should spawn just as u get there) should be easy now

Blue buff,
once you finish wolf camp go to the blue golem buff, if someone on your team needs it let them have it, if not go ahead and take it, use health pots on this fight.

GANK as you please, form this point on juggling should be fine, especially once you get your wriggles lantern



Dragon: once you get wriggles lantern you want to put it in front of dragon making sure the enemy team doesn't take it, any point after then you can take dragon with/without your teams help(help is preferred)

When banking make sure to let your team know what you are doing first.

First Agree on a target, normally you want the lane to over extend to bank but sometimes you don't need them to.

Make sure to land your Q, it helps the gank tremendously. as soon as u get near the champion with or without Q double use E to slow him down, if you don't think you can kill him before hit gets to the turret you may want to run in front of him and Use Dragons Rage(R) to get him further from the turret.. almost guaranteeing the kill.

Now for the reason i love playing lee sin.

There are a few tricks you can do on lee sin.

1.)Remember you can Safeguard / Iron Will to wards!!!!! so always carry some around and if you get in a rough situation put one down over a wall and simply jump to it!
2.)This is my favorite, if you are getting chased or ranked by the enemy and can't Safeguard / Iron Will out, simply look for the nearest mob and Sonic Wave / Resonating Strike them through the wall. guaranteeing an easy escape.
3.) don't be afraid to randomly Sonic Wave / Resonating Strikethrough the jungle, you rely on energy so its not a big deal, who knows you may just get some blind kills,with the blind monk!