Build 1:
Pure DPS with a touch of defense. Remaining points are spent in Offensive Mastery for early game farming and to make way for your Q ability to connect with the enemy player.

Build 2:
Off-Tanky. Armor Penetration from the offensive tree combined with your runes is enough for the early game to get you some good damage output. The Defensive masteries and runes will make you tough enough to compensate for the damage you don't have compared to build 1.

Build 1:
The rune build consists of a large proportion of armor penetration and mainly extra HP to help you in the early games. Extra attack speed to punch in those Sheen/ Trinity Force procs as quick as possible.

Performing well early game will define how you will end late game most of the time. This rune build helps you with that.

Build 1:
This build offers great burst, movement speed and moderate HP. Pretty much anything you need and/or want when playing Lee Sin as a Main DPS.

Build 2:
My new favorite build for Lee Sin. I actually came up with this one while playing Trundle and tried it out on Lee Sin and it worked like a charm. Great defensive stats yet also great offensive stats via the Armor Penetration from your runes and masteries. You get a great deal of HP so you can be a bit more abusive with the enemy (and your own health pool). I've noticed with this build that players really seem to not want to focus you because of your health pool but later they will realize you are an real threat.

Team work wise Lee Sin can be very powerful. You can help your allies escape or secure a kill by using your ultimate in a creative way.

An example would be:

You're chasing the enemy and you are all evenly as quick and you probably won't be able to take him down on your own before he gets on safe land. Now if you use your Q ability to connect with him and use your flash to get ahead of him you will be able to knock back the enemy player with your ultimate back into the lane where some/all of your team mates are trying to catch up with him and decimate him.

Now if the enemy isn't too quick but is still getting away you could just use your Q, followed by your E and then you use the slow on your E to get ahead of him and you knock him back with your ultimate.

I prefer Flash and Ignite on Lee Sin because in the early game you really want to get some kills to get your Sword of the Occult some early into the game and afterwards to get some stacks on that item.

Flash really is a life saver pretty much throughout the whole game as you can use it as creative as you wish. It is by far the best mobility summoner spell for Lee Sin especially combined with his own spells. Ghost really isn't worth getting as your Boots of Swiftness and Trinity Force will give you more than enough movement speed.

Proper use of Flash can result in VERY game changing moments during any sort of enemy encounter.

I really advice not to change these 2 summoner spell choices as they pretty much shape the whole play of this build. Aggressive and maneuverable.