Now that there are new masteries, this build is much easier to finish. Before I was able to finish my core build in 20 minutes, but now I can easily finish it in 12.
1st build is your core build.

2nd build is my end game build - this will always be different depending on the other team/ your team's team composition.

3rd build is if your team is doing well, and has no need for another tank.

4th Build

Well janna only has 1 offensive ability, so if you were to build ap all you could do is shield and ult to heal.
When i play i only use the ult to push people away and the shield is used for the +AD it gives. With this, i build all gold/5sec items and then buy so many wards that you can see the entire map.

Building janna this way would make it so that you are full utility, and if you can see the entire map, it could greatly increase the chance that you will win the game because theres no such thing as a gank when you see them coming.

Promote - So you can push lanes easier
Heal - You can heal
Clairvoyance - Sight
Flash - Mobility

1st set: Early damage for your lane buddy, and pushing power with your q.
Greater Mark of Ability Power - Ap
Greater Seal of Ability Power - Ap
Greater Glyph of Ability Power - More Ap
Greater Quintessence of Ability Power - Even more Ap

2nd Set: Same thing except with more gold.
Greater Mark of Ability Power - Ap
Greater Seal of Ability Power - Ap
Greater Glyph of Ability Power - More Ap
Greater Quintessence of Gold - this will help you finish your build much faster.

Your core build is up there ^^

but once you get all the items and ****loads of wards, start building resistance to w/e is killing you. meaning, when you die, actually look at who is doing the most damage to you then build resistance to that.

Basicly, your a tank with wards.

Start the name normally by waiting 10 seconds then CV their base calling out who is going to what lanes. Then cv their blue to see if they are defending it or not.

Unlike other supports, when you lane with janna you want to last hit the minions. I believe that split between the 2 people at bot, we should have perfect CS, making it so that noone can complain that your taking minions.

ALWAYS GO BACK WHEN YOU HAVE JUST ENOUGH MONEY TO BUY THE NEXT GOLD/5SEC ITEM

Never last hit champions unless you know your team can not finish the kill safely.

When a team fight starts walk into the middle of the enemy team and position yourself so that you can either
1) Reset the fight after the enemy team used all their skills
2) push 1 or 2 of the enemy team towards your team to be focused and the rest out of position.

After you get full build and have about 2.4k gold you should start thinking about buying resistance so that your more tanky.

Always ward EVERYTHING. by the end of the game im usually at the top of the gold charts, and bottom of the cs charts.

This + EVERY SINGLE BUSH CAN BE WARDED