This is a DPS build for twitch. There are two ways to build twitch which is AP and DPS, I prefer DPS. Twitch is a very good champion for a more advanced user. I do not ssuggest playing Twitch as your first champion but if you desire to play him here is the best way to build him.

You need to start the game off by buying a Vampiric Scepter this gives you life steal allowing you to stay in lane longer. Now i suggest taking the middle lane so you can level faster and begin ganking earlier. For your first ability you want to get is you expunge which allows you to do more damage early game and i recommend leveling this as fast as possible. At the beginning of the game Twitch is a VERY squishy character, he can't take a lot of damage, so you need to be cautious. With Twitch you arent going to be able to get an easy first blood unless you are in lane against another squishy character for say Teemo or Ashe, but most of the time you just need to wait till you are level 3 or so. Once you get enough gold you need to go back to base and buy your Executioner's Calling, I buy this item just for an early advantage because it gives you critical strike chance and life steal which again allows you to stay in lane longer. By this time you should be level 6 and have your ult. The most effective way to use your ult is to let the enemy push close to your tower then go invisible walk behind them and use your ult to just obliterate them. It is also good to use your ult when there are minions because you ult passes through everything it hits allowing you to hit multiple targets maximizing your life steal.

One of the best things to do with Twitch is ganking. You cant start this process until you get boots of mobility. The key to effective ganking is to be swift on moving from lane to lane because a good team calls MIA so if you are swift they might not get the chance to run. The second part is if you have a more than just two people in on the gank three v two normally works. So when the enemy team begins pushing a lane hard just call your team in for a gank. With Twitch you go behind the enemy while stealthed pop your ult and initialize the gank. If they start to get away just use your slow and don't use expunge until last sec otherwise it will just be a waste.

This build is not finished but will be completed soon. I will be adding game play videos for each chapter that I discus. If there is any questions so far or anything that you want me to add to the build just comment.