I do these builds in hopes that I help guide someone into learning a new or more efficient method of playing a champion. Any feedback or rating of any kind is appreciated as I do my best to guide players.
Any Votes, Ratings, or comments will be addressed asap and criticism is as welcome as praise.
Enjoy the guide.
As a side note, it is important to note that you will need to build reactively to be the most effective as Shen. His items ultimately decide his usefulness to your team.

This is and older guide that I am updating as I am seeing Shen appear more in the meta due to his super strong kit and his usefulness as a tank. I am creating two builds for Shen: one for jungle and one for Top lane. If this build does well, I will make another for support Shen, so make sure to vote and comment.

Trinity Force is your damage as top lane shen. Now that it's been updated to have 20% CDR and more attack speed, this item literally has Shen's name written all over it. You need to rush this whenever you can, but you might need to make the decision to finish a tank item before finishing triforce. You should build phage first when building the triforce, then the Stinger.

Sunfire Cape has too much damage to pass up on Shen.

Spirit Visage/Banshee's Veil for magic resist and health

Steraks makes your Triforce do even more damage on its procs and helps you survive in teamfights.

Titanic will help with waveclear and also help your burst faster.

Frozen mallet is a great tool for peeling and chasing as shen can easily catch enemies with his E, and give his allies time to catch up with Frozen mallet's slow.

Ninja Tabi/Merc Tread depending on enemy team comps.

For runes, I take some scaling CDR glyphs for 10% cdr at level 18 and some flat Magic resist glyphs. Armor yellows. Attack speed and magic pen reds to help apply more of your Q damage. Attack speed quints for aplying Q %max hp damage.

What is Shen's new combo?

Shen has the greatest dueling power against Auto-attack champs like Tryndamere or even Garen due to his AA block on his W (Spirit's Refuge).

Very Important Note!

In order to be successful with Shen, know everything about his Q (Twilight Assault). It has a slow that applies as an enemy is hit with the blade as it travels to Shen, gives a % max health as magic damage on hit, and lasts for 3 auto attacks. Also the bonus magic damage on hit is greatly increased when you pass the blade through an enemy champion. Also note that after you have maxed out this ability it is almost off cooldown after you have used the 3 empowered autoattacks. Keep in mind that you can continuously use your q after it gets off cool down at later ranks because each empowered autoattack that hits regens a significant amount of energy from his E passive(Shadow Dash).

When you Combo the order is as follows:

E > Q > W > AA

It is relatively Straightforward as your E (Shadow Dash) taunts for 1.5 seconds, Q (Twilight Assault) gives him a % max health as bonus magic damage on hit, and his W (Spirit's Refuge) blocks auto attack damage and crowd control from autoattacks. A side note is that even things like blitzcrank's E knockup is blocked while the in the protection area.

When using W (Spirit's Refuge), make sure to actually wait and see your opponent start to auto-attack before activating this ability.

Here's the thing about masteries I need to clarify: Take what you feel is best, this is simply what I believe to be the strongest on Shen. Strength of the Ages give you 300 bonus health, which not only aids in laning phase, but means you are even tankier in the late game.

Pros:

Strong for entire game
Huge Level 2 power spike
Does % max health as magic damage with his Q which is great against tanks
Passive shield is extremely advantageous when trading
Good base stats
Great for engaging
Fantastic global presence with ultimate
Great at chasing

Cons:

Absolutely no sustain
Lacks any sort of poke, meaning he must initiate a fight to deal damage
Only two damaging abilities

USE YOUR Q TO FARM

There is a tendency as we try to get better at the game to not use abilities to farm in order to have more mana to be at an advantage against a lane opponent. After you have unlocked E, you get a passive energy regeneration every time you hit an enemy with either the E dash or the Q bonus damage. meaning you can continuously use Q to farm minions as long as you use each of the 3 buffed auto attacks. This is your main source of damage and the bonus is truly massive. Also it is difficult to build against a Shen that is ahead since his damage is close to 50/50 magic and physical.

Ultimate Ability: R (Stand United) This is my favorite ability on Shen and for good reason. It can be used to save a teammate about to die and turn a fight around or it can used to protect an important carry on your team.

How to work as a team: When you reach the "teamfight" stage of the game where both teams are grouped together normally in a lane, your job is to punish a bad engage by the enemy or to catch an enemy with your E (Shadow Dash) to let your team collapse on a single target. Also make sure to use your E to protect your own carries from assassins like zed or talon.