Here as in most build you have Jungling/Nuke/Lane/Tank. I will be helping you decide if you are strictly support tank or support/tank/carry.

pretty explanatory. I shouldn't need to say much about these. Mostly to help me sustain the damage from champs a little better then other squishy champs. Plus at level 1 I wont me be melted by stuns and bad measure ability power users like stacked Annie. I have more health and armor then anyone I'm laning against. This helps me lane longer heal more and just set the bar for the enemy.

I grab the cloth armor and 2 potions of each health to heal me if i do get massively damaged early from the bush. And Mana to use if I spammed E to help get first blood and need the mana instead of wasting clarity. With the runes ability of Q to heal yourself and clarity for mana. I stay in lane almost till level 6 or as long as I can (Laned to lv 12 with just a shirt), either helping get my partner kills or me simply getting lucky and killing them myself. By first return you should have enough for Guardians angel and at least Ninja Tabi. Then you can help take damage longer an got Guardians angel as a crutch to take more damage. Rest of items vary depending on enemies. I always get Warmogs for the health. The Frozen heart is a must thou because of armor mana and attack speed lowering aura. The ceptar helps out really good to.

I go for Teleport because it easier to help protect lanes if they are Ganked hard. Also to get to your turret faster in beginning to stake out the bushes. Clarity for me is a must so you can sustain longer and more mana means easier to farm with Q for health. You could switch clarity with revive if you wanted to come back to life faster but I feel isn't necessary. I don't go for flash or cleanse or surge really don't need them offense needs the more charging moves then I do. Ghost can be switched for teleport if you need to get through there defenses to ult.

Something cool you can do is when engaged in a team fight. DO NOT use your ult until, after there stuns and silences have been used. Its much easier to get them in it to slow for teammates and dish damage out on them. Also in early game at level 6 when u see them charging at u unknowingly into your bush use ult so when they enter they don't have enough time to react get caught and damaged while your laning partner kills them. Also you can waste your ult to save a partner. When running from a group of enemy champs or 1-2 that are stronger but not as fast. Look around if your laning partner is slower step back hit the enemy with your E and run and continue this until you know your teammates is safe.

When with melee always be sure to lead with E and hit your laning partner with W. One so the enemy is slows and two for your teammate to hit better. Ranges if they have a stun let them engage then u hit with E and follow up with you buffing youself with W while your teammate hits the enemy. Also always let them get last hit if they are able your the tank your items don't take much to build. They on the other hand have pricy bills to pay and a fed carry is a happy carry.

In short, this is a straight up tank/support class. I have yet to find a better champ then him and I feel Nunu doesn't get enough support. I don't see him much besides getting bashed in bots. He deserves some reviving and that's what I'm trying to do. I truly hope my build and answer are helpful if you need any help or creative response. Or even ways to help me improve, PLEASE comment below