Hi guys, this is my first build guide for any champion, so be nice. After Shen's buffs, he's a really powerful top laner and bottom support. He is also really good for ganking and staying alive. This guide will focus more on top lane and how to gank efficiently, and not really on the jungling aspect of Shen. Shen is a good jungler, but in solo queue there is always a better jungler who can get around more easily (Skarner, Lee Sin, Mundo).
Teleport is more of an early game thing, if you feel that you have too much gold from a high creep score, you can recall then teleport back into your lane. Other usage for this would be that if you are in your lane and you see a fellow teammate getting beaten on, use Stand United, save the teammate, recall, then teleport back into your lane.
Flash is good for many things, the best way to use it would be if you are fighting someone soloing top, and they manage to get out of your taunt's range, flash to them and taunt, then finish them off with a quick vorpal blade.
Boots of Mobility
First off, if you want to be an effective ganker on Shen, Boots of Mobility are the way to go. I like these boots because they make Shen agile and fast just like a ninja should be. These will allow you to pop your stand united with a load of movement speed, allowing you to taunt and get a free kill/assist. These will also help you get into position much easier, when initiating team fights or 1v1's in the top lane.
Aegis of the Legion
This is a really major item on Shen, it should be one of the first item purchases. This item has a real impact in team fights, it's high MR and Armor make it so that your taunt is doing it's job well. Not to mention the support buff and HP it gives.
This is a really situational item, depending on the enemy's team comp this may not be as good compared to a MR item like Guardian Angel or Aegis of the Legion. The active does really help out in a team fight, granting you a sort of Amumu ulti, slowing down their team.
This is another major item for Shen. Getting this early allows you to stack it up while farming your lane for CS. Also, the HP of this item is really huge, allowing all of your abilities to do much more damage and make ganks much easier for Shen.
This is another situational item, giving you a lot of armor and MR, and allowing you to resurrect once every 5 minutes. This is a key item for him, depending on their team's comp, it allows you to be a little bit more dangerous in team fights and while pushing. The resurrection is really valuable. If you are engaging on a squishy AP carry and you end up dying, you have GA which will rez you and either allow you to pursue further or fallback.