Hey guys on Mobafire. This is a build i tried and succeeded, after i continuously played the build. Its very effective and I will add in extra details when i get the time to since im very busy with other works in life =p. PLease rate and if u downvote - please leave a comment and I shall reply as soon as possible. This build focuses on lifesteal, critical chance/damage and a final survivability item - all of u r pretty familiar of as 'Guardians Angel' ^^. So pretty standard and in similar item queue as other builds but different nevertheless because this build gives the player a simpler and easier approach to early game while playing Twitch.

Pros:
Is a very good ganker
Can easily disptach of squishies and dish out massive damage
Not as susceptible to oracles or wards if u play his cards right
Poison is a very effective last hit killing ability

Cons:
Very squishy
Has no 'real' escape besides hoping ur invisibility is not on cooldown or if the enemy beat u down before u cloak
Useless if taunted, stunned, blinded or slowed. [especially aoe/stun ultimates like Galio or Amumu
Will be targeted down if seen

Runes are pretty standard - u get critical chance for all the basic marks/glyphs and seals and then to top it off, u burst off with quite alot critical damage just for that extra ooomph!

I take exhaust for the slow and blind to shut off dps champions or to make my escape. It helps to give u time to hit those few attacks to lay the full number of poison stacks before u expunge. I take ghost with me to catch up to foes, attempt running away and to get those last hits on enemy champions.

It is best to max out expunge because that will be ur main damage dealer as it deals massive damage when u have substantial stacks of poison on ur target. U can gradually level up ur ambush to increase the time u can remain hidden. The slow is not as important but it is recomended that u put at least one point into it before maxing it out during ur final levels.

Like i said in the Introduction, the items are pretty standard, just built in a different, easier way. U get lifesteal to stay in-lane for pretty much a long time unless ur like on 1-bar of health. I get just the first stage of boots because its enough to start ganking in other lanes with the extra crit-chance and speed from Zeal. I then get BF sword to increase my damage output because obviously attack speed means zilche without damage. I then finish the Bloodthirster for extra lifesteal and damage and that leads me to finish my Phantom Dancers. NOW the phantom dancers should make u practically inviniclbe with the extra crit-chance and attack speed + the bonus to movement speed. I then continue to build up my damage with Infinity Edge (everyone knows what this is for, ie. crit-damage is scaled up by 50% and u get heaps of damage output). I get another BloodThirster for EVEN more lifesteal and i can recover from 1/3 of hp to FULL hp with just a few attacks on enemy minions. I then finish my dish with a Guardians Angel just for the extra Magic Resist and a 'Save My Life' card to keep dishing out the killing sprees XD.

Twitch is very hard to play when it comes to key ambushing positions or lining up ur ultimate for effective aoe damage on all champions. It is best to line urself up behind ur allies so that u have protection while ulti-ing or line urself behind them, to block off their escape and pray ur team is good enough to distract them while u set off ur ulti. When running away, always try to attempt escape by using cloak, and that might open a chance to counter their attack by appearing behind them and smashing ur 'E' key for expunge to finish them off.
When laning, always try to appear missing in action so that ur lane mate can bait them out and u can start ganking them.

All in all, Twitch is a very enjoyable and well rounded champion and it takes some time in learning how he works. When to gank, when not to gank and looking out for suitable targets in the field or even which spot to line ur ulti up against a huddled group of enemy champions.

Have fun and hope this works for ya cos this is how i play him. I will add colours and pictures when i have the time ;D