Hi, I'm Swallow It Daddy, I play on the EUW server and my current elo is Gold.
I've started to play League of Legends a year ago so I need your feedbacks on my guide, don't be too harsh though.
This guide is kinda like a prequel, if you want further information, about the champion itself look on youtube or even the MissMaw guide, it's pretty complete even though our opinions are a bit different about the build itself.
I hope you'll enjoy this guide, it's the first one I made.

ENJOY YOURSELF !

These are the basics runes for healers/shielders like Janna, Lulu and Soraka. They benefit a lot from AP so that's why we run AP in glyphs and quints.
Nothing much to say.
If you're playing against AP supports that pokes a lot like Brand or even Zyra, I suggest you to put 12 MR in your glyphs, it's really up to you.
By the way, I put scaling HP, not flat, the reason being at level 6 I will have the exact same health as if I would have put flat health (72hp). You just have to play a bit more passively before your level 6, your first powerspike.

First, let me explain the build, its purpose.

Janna, Lulu, Soraka scale very well with AP, this is mainly why I use this particular build.
However, we can't build a support like them full AP, it just doesn't work at all, plus, every support need sightstones.
I started to do some research to find the best build that could fit Janna, Lulu and Soraka.
That's how I came up with this build, I'm going to go further into the details for each item.

Even though Ancient Coin is pretty strong at the moment that (even tanks pick it instead of a Relic Shield), I pick Eye of the Watchers for some pretty obvious reasons :
- the sightstones to put vision all around the map everytime;
- it is the only AP item you can get (with a sightstone), otherwise I'd have picked Eye of the Oasis;
- it gives health, mana regen, golds, and cdr.

We pick boots of Mobility because with my build you already have max cdr without the Lucidity Boots, plus you're so fast that nobody can catch you, and even though they break its passiv, you'll still end up with a lot of mobility (MS) to escape most of the situations.

This item is A MUST HAVE on every shield/heal champion, you have to buy it, both of its passiv are incredibly good, plus the item provides AP, cdr, mana regen and a boost of movement speed.

Another good item which provides good raw stats like health, cdr, mana regen (and ofc its passiv) but the most important part of this item is its active, despite of the precedent nerfs this item still remains a very good item, it finds its utility in teamfights where the healing is pretty huge and can turn a fight around.

Since last changes to this item in the patch 7.13, it has become a very good item which now scales with mana regen (it gives you now more AP), once again its raw stats are good : AP, cdr, mana regen and MR. Its passiv allows you to heal your team mates up to 250 hp, which is always useful. This item is very important as well in my build so don't skip it.

Now, why this item ? Well as I said earlier, these champions scale very well with AP and since in every item we have AP (plus in our runes), it will significantly increase our shields/heals.
If you find yourself against a team which has a LOT of CC, you can buy Mikael's Crucible instead (I almost never buy it anymore).

If I had to sum it up, I'll do it this way : this build gives you a lot of shield/heal power, peel, engage, disengage and you are pretty fast.
You will be pretty squishy overall. This means you will have to play carefully.
However, NEVER forget to harass your opponent since you earn gold mainly while harassing (remember you have Spellthief's Edge). If you think you'll take too much damage to harass them with an AA, you can use your Q spell, try not to be out of mana though, manage your mana pool carefully.
Soraka and Janna don't do much damage, even with this build (well, maybe Soraka's Q) but Lulu can really hurt (especially late game), because she has defensiv but also offensiv abilities (her Q and E even though you should keep your E for your allies).

The combination of the runes, masteries and items will make you a real pain in the arse for the ennemy team especially if you play Janna ;) ;)
Remember that utility supports are better in this meta, don't underestimate them ! NEVER !

Good luck in your games summoner !