So, after I've used many guides here myself, I finally decided to create one myself. So this is my first guide here, and I have decided to make one about Lee Sin. The reason for this is because I in some way have been facinated by him, and gotten pretty good results when playing him.
Hope you like it!:)
Random Updates About This Guide
Sooo. After I recieved a comment about the amount of stuff in this guide, I have decided to explain myself, so that I won't recieve more comments saying "you need to expand".. This is my first guide! I am still learning how to do all this, and therefor there will be updates and expansions, but it takes time. :)
 I start with Doran's Shield this is because I in early game would want to have some survivability, and substain lane for as long possible.
 When I finally go back to buy or regain health I pick up Boots of Speed this grants me some mobility, and later on this will help a lot.
 Now I pick up Wriggle's Lantern to get lifesteal, armor, damage and a ward every 3 minutes. This item will help me substain lane and also ward so a jungler don't run up and kill me every time he is around.
 Now I upgrade my Boots of Speed to Mercury's Treads. This will grant me both tenacity so stun and slow ect. durations is decreased. This will help me get out of situations where I usually would either have died or be forced to recall.
 Now I get Frozen Mallet. This is a big boost when getting into fights, because it gives me a boost of 700hp and also a little bit of damage. But besides this it also lets me chase down "prey" easier when they try to run away.
 After that I get Maw of Malmortius, this is a big help when I try to either deal damage or avoid dying. It gives great survivability because it makes this shield.
 Finally before i exchange my Doran's Shield i pick up The Bloodthirster. This item lets Lee Sin deal tons of damage, and quickly eliminate an enemy. Also it gives great survivability because of the massive amount of lifesteal that it gives.
 I change my Doran's Shield with Trinity Force, I could also have changed it with an item that gave more survivability fx. Randuin's Omen but I prefer to get more mobility so that it's easier to chase down enemies that is running away, and also it helps escaping. Besides all this it also gives a little amount of damage and ability power, which will help in fights.
 When this is done i exchange my Wriggle's Lantern in something more usefull in late game, because you don't really need the ward anymore, and the damage and armor is a little low when in late game, so you would want to exchange that with something better depending on the situation. When you have problems surviving and you are dying too often by something AD, you can replace with Randuin's Omen (if you haven't already gotten this item instead of Doran's Shield. Or if the opponents is building much armor, you can replace with Last Whisper to get armor pen which will really help out when having trouble dealing damage. And if you are doing fine against AD opponents, but the problem is AP, then you can grab Guardian Angel this item though is good agains both AD and AP.
In Depth With Items
I do know that i explained some of this in the "Items Explained" section.
Mecury's treads are GREAT when trying to survive without getting trapped and then jumped by the whole enemy team. It gives amazing survivability.
Those boots are just as amazing as the Mercury's Treads, and 10% damage reduction is actually very much, and besides that these boots gives 25 armor. When against enemies that deal too much damage this is a great item to pick up.
This item is almost a must for a jungler, and also when solo top this item is great! You don't have to waste money buying wards, and besides that this item gives nice bonuses in: lifesteal, armor and damage.
This item gives a great boost when you are solo top, because the item gives you everything that you will need to survive and get kills.
This item can be picked instead of Frozen Mallet because it serves the same purpose, you gain very much HP and can substain lane longer. But it does something else. Frozen Mallet is better when you need to do more damage too But Warmog's Armor give you a very good health regain too, so that you will last longer in lane than your enemy. This will help getting lvl advantage and winning lane.
This item is extremly good for both surviving and dealing tons of damage. And against AP this item is priceless! It grants you a shield that will take care of 400 magic damage each 60 seconds. And also it grants you 55 damage and 36 magic resitance. This will be very usefull when chasing down enemies and when escaping situations that looks bad.
This item is a must when you want to take down enemies like flies. The will fall before you, when you are armed with The Bloodthirster!
Well.. You could buy this, but I really won't recommend it. I prefer The Bloodthirster because a) it deals more damage and b) Lee Sin don't brawl, he uses abilities do deal most of the damage, so critical chance and damage is not the thing that he needs the most.
This item is also good for Lee Sin, because it gives him everything he needs to be the perfect warrior. Ability power, attack damage, movement speed, very little critical chance, health and USELESS MANA!
This item is also a good alternative instead of Trinity Force but it dosen't give the same bonuses. This item is more focused on surviving. This is better if you prefer to play a more tanky Lee Sin.
These are just some tips when playing Lee Sin, I do know that some are obvious, but not everyone know everything about this champion, so I have decided to make a "NO!" section, so that you know what you don't want to buy when playing Lee Sin.
 Lee Sin uses energy. This means that buying mana and mana reg is useless and a waste of money. Don't bother wasting gold on this.
 Lee Sin isn't going to be needing critical chance and damage. This is because he uses his abilities to deal most of the damage.
 Do not buy ability power for Lee Sin, the only ability that will be granted a bonus by this is Safeguard.
 Lee Sin does not need a lot of movement speed in early game. This is because his abilities Safeguard and Sonic Wave makes his mobility high. He can jump basicly everywhere as long as there is either an enemy, a hostile minion, a friendly minion or an ally champion.
I know that these results aren't the best results ever, but these are the most recent results. I will be posting more results as this guide expands (if you guys like it!).
As I said before i will continue too post results. Here are my most recent ones :)