Welcome to my Lee Sin guide, this is my first guide here on mobafire but I feel that Lee is one of my favourite champions and I wanted to share my build for him and hopefully help some new and maybe experienced players find a build that works for you.
As Lee sin is, in my opinion, one of the hardest yet most rewarding champions to play I would suggest having at least some knowledge of LoL before trying him out, and remember, it is just a game. Have fun with it and if Lee Sin is not the champion for you, then thanks for reading this far.

Please note: This is a Work in Progress. I will be adding to it over the coming weeks.
EDIT: Since the nerfs on Lee I have not been been playing him as much, because Riot obviously feels the need to nerf all the champions that do not need nerfing. Now I'm not saying Lee is a bad champion, he can be a great addition to the team, But Riot seems to only care about profit as they send out new champions every 2 weeks while the old ones rot away to become nothing. Hopefully I will finish the guide eventually but for now I don't want to play a champion that riot clearly does not care about the fans of.
please note: I know the nerfs on Lee do not make him unplayable, unlike the nerfs on Irelia. And as much as I enjoy league of legends am becoming more and more annoyed with the choice of updates in the patch's. So, if you thought 'TL;DR' to that, my rant is now over. Please continue to read the sections about Lee Sin.

For runes I choose armour pen. marks Greater Mark of Desolation and armor pen quints Greater Quintessence of Desolation for taking down tanks and armor stackers such as Nasus , Rammus , Amumu , and so on.
Next I choose armor seals (Greater Seal of resilience) for that extra defence.
Magic resist glyphs to stop those pesky AP casters early on, and if you still have problems later, check my item guide for situational defences.

For my masteries I choose 21 / 9 on offence / utility. Of course Lee sin can be built in many ways if you want to go 9 / 21 Or even use the defence tree and build even more tanky then find what suits you best, this is just a guide not something everyone must follow.
Why I choose the 21 / 9 masteries is because I want Executioner , for my Resonating strike, 6% more damage on enemies below 40% health is a huge advantage and if you hit them with the Sonic wave / resonating strike combo while they are fairly low HP, it is a certain kill.

-Lee Sin is a very durable and versatile guy and can be played either as a tank, off-tank, or DPS build
-No Mana :)
-Lee Sin has great skills including a knock-back kick with great AD scaling
-You will feel like a boss if you finish someone with resonating strike from a long distance.
-Lee Sin is a bad-*** blind monk

Cons
-One of the hardest champions to play effectively
-Close range for the most part, does have a nice gap closer though.
-Relies very much on skill shots / good placement for dragon's rage
-Pretty much a snowball champ, if you have a bad start, most of the time its game over for you, or you will be very poor in team fights late game.

I prefer to go full offence on my skill sequence and choose to start with sonic wave for that early harass and finisher with resonating strike.
Then I take tempest / cripple for the slow and AoE minion farming because before you get the Wriggles lantern I feel Lee is a below average farmer with just basic attacks. If for whatever reason the opposing team have a much better harass early game. Then I suggest getting at least some safeguard much earlier as the bonus lifesteal it grants you will help sustain your lane. But the 5 health potions at the start should prevent you from needing it, and then the lantern should do the same.
With Lee Sins dragon rage skill, your opponents will be kicked in the direction you are facing, so if you can slide past them and kick them towards your towers for some easy kills.
Please remember, only follow the skill sequence I have shown if you are doing well. If you start to die, please trade some points from cripple to safeguard earlier.

For the summoner spells I almost always go with the flash / ignite / combo for escaping or chasing those final kills. If you have not unlocked flash, I can only suggest ghost or exhaust. I am not a huge fan of any other summoner spells and especially on Lee Sin would only ever take the 4 I have previously mentioned.
Also remember, Lee sin does not have mana, so NEVER take clarity.

I have only ever tried jungling on Lee Sin a few times, but he is an exceptional jungler and has great ganks especially early - mid game. The build shown would work perfectly well in the jungle. For jungling I would recommend reading a jungle only guide until mine is complete and I gain more experience. (Currently working on it)

For items, I almost always start with cloth armor and 5 health potions . I try to sustain the Lane to at least level 6, but if you need to recall, try to at least buy the Madred's Razors for the minion farming. Some people may prefer to choose the Doran's Blade or Doran's Shield as their first item. Which is an acceptable choice but I prefer not to as it does not build in to anything and will be sold later.

With the items I almost always follow this build until you reach the black cleaver which is were I insert my situational item, if they have lots of AP casters, drop the cleaver for a Force of Nature. If they have tanks, stick with the cleaver, if they have HP stackers like Cho Gath or Dr Mundo, pick up a Madreds's Bloodrazor for the passive bonus. If you have the money and the game lasts long enough, trade out Wriggles Lantern for The Bloodthirster . Learn how to adapt your build to counter the enemy team and you will be dunking in no time.

Well, I hope you at least try this build and comment. I will try to add more new content the more I play. This is the first guide I have ever wrote so if there is mistakes or anything to add, please feel free to tell me or ask any questions and I will try to update accordingly and hopefully with your help we can make a great guide for the master that is, Lee Sin.

I do not have many people to add to my credits but I would say thanks to Alex for telling me to buy Lee Sin and to Jack for helping me ensure my skill sequence is correct. Dale and Ryan for letting me use Lee Sin to kick them in the jaw for practice and being my online team. Keep on dunkin'