I still don't understand what this build is promoting?
CDR+Damage?Well,that's one way of playing support :/

Runes are wrong.As usual on any support it should be GP10 Quintessences.
Marks can be Magic.Pen,but in my opinion has a main support i prefer extra armor marks there.

Masteries,26 points in utility.Waste of points.
9/0/21 or 0/9/21.Would be way better.The first to promote your....pokey playstyle and the other to reflect the current support meta.

Now there is something i truly need to point out.
Boots,then Tear,then Philo then Kage's and then Sightstone?
Where the hell is the money coming from? I would have that philo at 20 minutes if i followed your build.

If you really want that Tear it should go like this.
Philo,Boots/Sightstone,Tear and the kage's. If Philo isn't enough to keep your mana something is very wrong.

As of the Build,all i can point out is Seraph's Embrace and Morellonom?
On a support?No no no no. Locket of the Iron Solari+Another Aura and you are golden my friend.

Especially because 68 armor and 87 mr coupled with 2200 hp is set to destruction.
Oh and the fact that you NEVER build the exact same build has support,teams have different needs,different enemies.

This guide being from a Diamond Player,i would expected better.
It may be your playstyle and it might work for you.Let's hope it works for others.I dished it just using my support experience.

Also on a closing remark.Playing support is about what your team needs,not what you need.Else why would most support builds consist of mostly the same cores and auras.AP Mid Zilean might need max mana+regen.Support Zilean needs some regen and auras,for his team.

Not too bad. You pointed out well Zilean's weaknesses as support, but I don't see you build solving nor attenuating them. Your cooldown reduction approach is good, though.

Other people already pointed out: Tear of the Goddess is not necessary. Your philosopher's stone and Chalice of Harmony should be enough.

Zilean need hard mana regen + good max mana. Morellonomicon gives good mana regen. No need to replace it with Frozen Heart. Will of the Ancients, Twin Shadows this items give you 0 mana regen and 0 max mana. Zil no need them. Shard of True Ice gives you only 5 mana regen per 5 seconds - so low.
W/o Tear of the Goddess Zil have so low Max mana.

Im not talking about item builds.

You said that you never should use Q lategame, but I beg the differ :P

100+ magic resistance = 50% damage, right? Not to mention non-supercarry champs will have over 150 MR. 320 damage is still something, but it only shines if you can hit multiple people at once. Still, that doesn't justify building AP over aura, because you won't have the gold for it and aura items are more effective to support your team. Still, some AP support items like Will of the Ancients, Twin Shadows, Shard of True Ice and Morellonomicon can be usefull, but shouldn't be the main priority, rather more situational.

Item list like:

Ionian Boots of Lucidity, Ruby Sightstone, Mikael's Blessing, Morellonomicon, Shurelya's Battlesong and replace boots. One spot has to be left open because of Vision Wards. Sounds similar to the actual build, except for leaving the tear out which you don't need anyway. If you rather want a 6. item, a tank item could be good. Of course, you can build many different items in an order fitting the situation. You can go for example tankier with Frozen Heart instead of Morellonomicon.

640 aoe damage should not be underestemated, late game or not :P

The reason why Zilean can be good as support is is earlygame superb harassment and his lategame 10 sec ultimate potential. Lategame his damage is more or less **** anyway, so why not just focus onto aura items to help your team. Combine this with CDR and you got it. Lategame, you don't have to use your bomb anymore anyway, which drasticilly lowers your mana cost.

+ Zilean's passive does the job anyway.

I know it's been mentioned, but I think Chalice of Harmony and philosopher's stone should be enough mana regen. I don't think Seraph's Embrace is that amazing of a luxury item anyway. Have you tried Liandry's Torment or Zhonya's Hourglass in its place as a late game AP item?

Also I suggest picking up Summoner's Wrath if you're taking Ignite. Free offensive stats on a ranged support is really good. You should be able to sacrifice a point from Awareness , it's a pretty mediocre mastery anyway.

i don't play zilean to be honest but i can say 1 thing based on my little experience as supp:
you generally won't afford to upgrade your Tiar(not in terms of stacks in terms of gold) so if you need mana there are better choices like Chalice of Harmony(it also provides you with MR) or Mana Manipulator.
also het GPS quints

i can't -1 cuz i don't have much knowledge on zilean

He means how are you diamond when your build is so ****ty.

Again? It mean i was diamond than lose it than i diamond again? Wtf