This build gives you a nice fat tank build that focuses mainly on being as beefy as possible.

For runes, you could just take flat health everything, but armor and magic resist are better overall items since they work to bring damage down. Every point of armor gives you 1% extra health against physical attacks, likewise with magical damage. So really armor and magic resist sort of scale with level as well, not just flat health that stays the same throughout the match.

Focus on getting Tenacity mastery in the defense tree, this is my only advice. The rest can be whatever you like. I like taking ghost and exhaust because they aren't far in on the trees so it's easy to get its bonuses.

Doran's Shield should get you a head start and let you farm better. Get Mercury's Treads and Heart of Gold early. Treads gets you your movement speed, though dash makes movement a lot easier, especially because Shen uses energy instead of mana. The main point about getting Mercury's Treads is getting its Tenacity, which is extremely useful for a tank. Heart of Gold early builds into Randuin's Omen; and gets you more gold the longer you have it, so it's best to get it early. Grab Randuin's Omen if the enemy team's physical damagers are doing well. Grab Force of Nature instead if the enemy's mages are doing well. After you get both items, get Sunfire Cape. You should be durable enough by that point to walk by jungle camps without getting damaged badly. After that, it's completely up to you though I just build some random tanky health items like Warmog's.

Vorpal Blade is a great tool for Shen. It's heal is for all your allies which means you and your laning partner can get some heal without having to recall. Max dash afterwards before feint, the reduced energy will make a big difference. Max dash second UNLESS you are struggling or behind. In those cases, max feint first for survivability and more defensive play. And as usual, get points in your Ultimate whenever you can. When it's maxed, it becomes a true game changer. In the first and second level it sometimes is inefficient but can still make great saves.

Summoner Spells that are good:
I personally take ghost and exhaust, partly because they are high on the mastery tree not requiring any amount of previous points to get.

Ghost: Increases your survivability and able to catch those enemies that you just can't quite snag with your dash.

Exhaust: Used mostly for chasing, ghost is for escaping. But if your running from one enemy, exhaust would be a better choice.

Flash: Can replace your ghost or exhaust in catching up and escaping. Also has many other purposes such as ganking.

Smite: Only take this if you are jungling. Yes, Shen is a good jungler. Vorpal Blade and Feint make him last longer in jungle, and the dash can help you escape ganks. Your Ulti means you can get to team fights and save your squishy allies instantly from your jungle.\

Fortify: The idea here is to taunt an enemy and hit fortify so they take heavy tower damage. Now you can save your towers and save your allies.

Bad Summoner Spells:

Clarity: Probably the worst idea since Shen runs on energy and not mana...

Rally: Pretty useless summoner spell all around

Cleanse: This is used best for your squishy friends and not a beefy tank like you.

Quick notes:

Revive can be good and bad: Firstly, you don't need the bonus move speed. But also as Shen, you shouldn't be afraid to die for your team so this can be good to get back into a fight right after you died. (Especially with your Ulti)

Teleport also goes either way: You have your Ulti which already makes you be able to jump to different locations fairly fast. Shen can get places pretty fast with his dash that can cut through walls in the jungle. Unless you are really crazy about mobility, don't get this summoner spell

Heal: Heal can be good in team fights and just when you need to stay in lane but have too little health to safely heal from vorpal blade. Maybe just to improve survivability. In my opinion, heal is not needed as Shen is pretty beefy and other squishy champs would probably take this. (Multiple heals in a row have diminished effect)

You really need to keep an eye on your teammates as Shen. Your Ulti is what makes you special and you need to utilize it. It can save up to five deaths per game if you are aware what's happening on different lanes.

Early game, taunting an enemy trying to attack your turret can get you easy kills. Try just putting in a last hit here and there without unloading extra damage unto the enemy lanes. This means they will slowly push to your tower and you can get some free farm. They will be forced to stay at a safe distance since you would taunt them instead. Great to deny the enemy gold and experience. Vorpal blade lets you last hit from a range despite being melee, which should make gold farming easier.

Despite all the moaning and groaning from everyone that Shen's nerf makes him useless, Shen is still one of the best tanks in the game and really can be an asset to any team.