Well, here we go my insane mind go for a walk with aggresive build of Lee Sin. It's made for maximum pleasure and fun of Lee Sin champion and playing mostly with style HIT & RUN tactics.

Generally this build is made for jungling and well performed ganks. Lee sin is character which is not so easy to play and you must find your own way to him. You can enjoy all of what he offers when you became part of his true purpose- and it is the assasination. Basically with Lee you are trying to turn enemy into hopeless slow-moving/attacking object which you can over-helm with your attacking speed with on hit effects of this build (significant boost of his passive -2 hits always between the casting of skills), higher armor, and as support using vamp for quick healing on creeps, neutrals... boosted even with W->W skill to really high value. He is best suited for 1v1 combat or finishing an enemy quickly, but lacks against magic and more enemies because his survivality is cornered on magic dmg recived and for that skill needs to be applied and really wise and calm mind.
MAY THE FORCE BE WITH YOU... ALWAYS.

W for first I think is best for beginning (in jungle improving his survival) which grants shield, armor + vamp (most of the time I double tap this, increasing your survivality and total health more than W,2 hits,W - exception are taking down the tower or when you need attack speed just to finish off someone- When I start 1v1 I also double tap). Later on, with more points vamp & spell vamp is on really good level even without any life steal items. Progressing with E is not ment for DMG (but have decent dmg) at first but considerred as really good way of slowing enemy, creeps (attacking slower). Q being assigned as 3rd skill is ment to prepare character to assimilate with any occured situation on battlefield, but dmg is also possitive and main feature of another teleport-like skill more significant when finishhing off an wounded enemy with second Q-Q (as additional +10% dmg of life missing).

AFTER LVL 6 It really depends on situationand needs of champ. For me it really differs from game to game

Runes are build to help deliver more DMG to everything that moves with MARKS of Desolation and QUINTs of same type.

Armor SEALS with one QUINT, lantern + BOOTS of ninja are together doing totall a lot of armor to shield Lee which can turn upper hand in combat and when you count in also skill W-W, well...

and finally Glyphs to boost Magic resist just a little bit and improve a weak defense against magic.

Masteries made for jungling especially (+ EXP gaining, buff duration), improving armor penetration(and other helpfull offensive masteries). 21-0-9 (He is not made to be tank so no other option than this)

Lee can be really improving teamfights with
playing on enemy's nerves with Q, 1-2 hits, Q, then W back to ally .
Help with running enemy as Q-Q, hit or two, E, hit E, then he is pinned and team can catch up, then just mind your own business with W, 2 hits, W, hits,etc. (to boosting your attack speed + maintaining health with life steal), if running even faster E,E, or just delivering lot of dmg instantly with Q-Q if lower health.
Catching the Fire ball is name of something what is basically known as really nasty move of Lee Sin. As assassin going from back, cast Q, hit, E, R dragon kick,, as he flies Q to teleport to him and then E to slow him there and finishing the job.

Lantern- for boosting yourself inside jungle, really decent life steal together with W-W skill, meaning that less often returing to base as he can heal himself on creeps. SIGHT WARD. well really good item.
BOOTS of Ninja- for this build providing more defense and also cheapest boots in store.
Trinity force- starting with ZEAL can be swapped for hammer- moving speed improved or slowing an running enemy (best for ganks). Trinity force basically must have items on Lee sin, passive- after skill 150% of base dmg- together with Lee's 7 skills and his passive can really fast things up against towers.

NOTE: IF YOU HAVE A LOT OF GOLD GO FOR BLOODTHRISTER, BUT ORIGINALY I GO FOR EXECUTIONERS CALLING- upgrade ZEAL to PHANTOM AND THEN AFTER I HAVE ENOUGHT MONEY I SWAP EXECUTIONER TO BLOODTHRISTER and build is complete.

Force of nature- give great magic resist and movement speed for this build as vital.
Hexdrinker - Also really good item for LEE to improve DMG and also give a little survivality against magic magic resist +30 and +300 dmg in case of less than 30% HP
Phantom DANCER- Mosty made for BOOSTING his movement speed, finally having summary make it 19 points under 500 but attack speed is now also significant and making perfect combo with Executioner's calling+ WIT's END (on hit effects) and consider + 50% attack speed with Lee's passive to it.