Pro's

-Good early game damage
-Map wide play making potientail with (R) Stand United
-Has crowd control
-Can engage or disengage with (E) Shadow Dash
-Always useful with percent health damage on (Q) Twilight Assault and utility
-Strong lane trading against ADC's with (W) Spirit's Refuge auto attack mitigation
-Benifits of a Tank and Enchanter

Con's

-Melee
-Will be less tanky compared to Top/JG Shen
-ADC inting while you make a cross map play with (R) Stand United

Primary Tree

Guardian

Shield to protect your carries that will scale with your bonus Health, Ability Power, and increase from plus percent Heal and Shield Power from items like Moonstone Renewer.

Font of Life

Will help Heal your carries and can proc off of your Slows from empowered (Q) Twilight Assault, your Crowd Control from your (E) Shadow Dash and Slows from your items like Iceborn Gauntlet. The Heal will also proc the Dream Maker passive and really ties everything together. Gives a Heal, damage mitagation, and bonus magic damage buff for your carry when Font of Life procs, so it is essiential rune when building Dream Maker.

Shield Bash

Strong damage rune that will proc off of any Shield on Shen and scales with bonus Health. Avoid taking when building Dream Maker. It pairs well with Bloodsong.

Conditioning

Extra Armor and Magic Resistance after 14 minutes to help Shen remain tanky into the later half of the game without having to focus on building more Armor and Magic Resistance items; thus, allowing for more Health and Shield increasing items.

Second Wind

Can be taken in poke heavy lanes to help survive the early laning phase with the extra Health Regeneration when it is proc'd.

Overgrowth

Allows Shen to stack bonus Health throughout the game to increase his tankyness and the strentgh of his Shields.

Secondary Tree

Axiom Arcanist

Gives Shen stronger and more frequent (R) Stand Uniteds during the game. Allowing for stronger agency and more impact in a game. Shen's (R) Stand United cooldown is quite high so managing to score a takedown after you use it will be high value. Probably around a 10-12 second cooldown reduction give or take depending on champion level and Ability Haste.

Transcendence

Gives more Ability Haste to mainly help lower the cooldown of your (R) Stand United.

Runes To Avoid

Aftershock

It has good burst damage and initail damage reduction from the bonus Armor and Magic Resistance, but with the long activation till the damage proc's it is too inconsistant -IMO-. Also you won't have access to the Shield from Guardian which will negate some of the power of from Dream Maker and Moonstone Renewer.

Ultimate Hunter

Typically a great rune for Shen but in the support role it is too inconsistant. You need to score a take down on each memember of the enemy team and as a support Shen and that will be difficult to do in most games. Rather it is better to focus on general Ability Haste, and ultimate haste from items like Zeke's Convergence.

Unsealed Spellbook

Very high playmaking potiential with this rune but will require high game knowledge and understanding. Would only recommend, if you are a high elo player. The risk/ reward for a lower elo or mid elo player will be too inconsistant -IMO-.

Support Item Upgrades

Dream Maker

Damage mitagation and bonus magic damage on Auto Attacks for your carries. Helps maximize the enchanter ability of Shen. Strong synergies with Font of Life, Guardian and items that Heal or Shield like Echoes of Helia, Mikael's Blessing, Locket of the Iron Solari, etc.

Bloodsong

With the Sheen passsive it gives good damage. Avoid building Iceborn Gauntlet with this as the Sheen passives overlap.

Solstice Sleigh

Games where your carry needs the extra Movement Speed to navigate fights and for picks.

Celestial Opposition

Games where you need to frontline more or the enemy has high burst.

Core

Zeke's Convergence

Such a strong first item. Has everything Shen needs for support. Health, Armor, Magic Resistance, Ability Haste, and Ultimate Haste. Cheaper and more stats than Bandlepipes.

Protoplasm Harness

Cheap with tons of Health to increase all of your Shields and general tankyness. Lots of Ability Haste for lower (R) Stand United cooldown and a strong item passive for suvivablity.

Moonstone Renewer

Massive increase to all of your Shields. Solo allied Shields will be HUGE and during team fights it will proc a second Shield to close allies, increasing Shens utility greatly. Some Health and lots of Ability Haste to further decrease his (R) Stand United cooldown.

5th Item Options

Riftmaker

When you don't need more resistances and want to focus more on the strength of your Shields. With Moonstone Renewer Shen's (R) Stand United Shield will be next level.

Bandlepipes

When you need some extra tank and general utility for team fights.

Heartsteel

Lots of Health and some extra damage from the passive. When you need to keep scaling as much as possible.

Warmog's Armor

Lots of Health with the ability to stay out and make extend plays late game.

Echoes of Helia

Extra Heals for your carries. You will need Font of Life to really make this work.

5th Item Armor Options

Randuin's Omen

Against two or more critical strike champions.

Unending Despair

Against a heavy tank and bruiser enemy comp.

Iceborn Gauntlet

When you need extra peel or against high mobility comps.

5th Item Magic Resistance Options

Kaenic Rookern

Huge Magic Resistance Shield. Best late game Magic Resistance item for what it does.

Abyssal Mask

Three or more Ability Power champions on your team. Best item to help your team.

Boot Options

Plated Steelcaps

Should look to buuld these against heavy Auto Attack teams when there are no heavy Slow enemy champs ( Ashe, Rylai's Crystal Scepter users]] or heavy Crowd Control comps. Most of the time; if, you are perma Slowed or perma chained Crowd Control then getting these won't matter and are worse.

Boots of Swiftness

Should look to build against high mobility comps and manditory against champs with heavy Slows. 100% you will NEED these against champs like Ashe, Anivia, Aurelion Sol, Zilean, and mages who like to build Rylai's Crystal Scepter such as Brand, Zyra, Mordekaiser, Singed, and Swain. Without these they will kite you once you engage and most of the time you can't escape either.

Mercury's Treads

Almost mandatory against heavy Crowd Control comps. Do not build for heavy Slow users; Boots of Swiftness are much better. If, the enemy comp has a mix of both, then pick your poison; really depends on how much Crowd Control they have vs how many champs with Slows. -IMO- more Slows is a greater threat overall then Crowd Control. Shen can survive a few seconds of Crowd Control but if you are perma slowed after and your (E) Shadow Dash is on cooldown... then gg, you will die.

Situational Items

Mikael's Blessing

When your carry needs a get out of jail free card to survive team fights. Synergy with Dream Maker as it will proc the passive; so when you use it, not only will it give Crowd Control removal and a Heal but also damage mitigation.

Redemption

Team fight impact with the item active.

Knight's Vow

When your carry needs the extra sustain in team fights. Strong synergy with Protoplasm Harness as Knight's Vow's passive will stop once you reach %30 health and Protoplasm Harness's passive activates once you fall below %30 health. So, Knight's Vow takes you down to %30 health, you take a little damage, Protoplasm Harness passive kicks in, you Heal back up above %30 health, and Knight's Vow's passive comes back online. Basically greatly extends the amount of damage mitigation for your carry Knight's Vow is able to do during an extended fight.

Locket of the Iron Solari

When your carry needs extra burst protection in team fights.

Zhonya's Hourglass

Cheeky survivability and play making item in team fights for Shen.