Just letting you know, CDR is almost useless on Sona except for her ultimate, because all of her main skills rely on that 6.75 second cooldown for equal distribution, the problem here is that it lowers the cooldown by 0.07 seconds with one item, not noticeaale since the game rounds it anyways. great build none the less!

Then I give you + :)

Alright. I've looked at the masteries, I did update to include presence of the master I agree that spell is going to more helpful longterm than 1% regen.

Rave- I'm still playing with the masteries. I've heard lots of suggestion about them, and I will take your comments into consideration when I update again. :)
You don't need more defense, I cover that all in the items section. You can either pick it up as a final item, or I provide several options to switch out with if you really want that defense. However, I find between flash, your heal, speedboost, and all the cd reduction, if you play smart you wont' need it.
I agree this is more of a dps build than a support build, but it works incredibly well as support that happens to do a lot of damage w/ the massive heals she throws out, as well as her clarity and speedboost. I find this is a more effective build for support than some of the other 'traditional' support builds.

i dont give + nor - because:

-1 point of presence of the master much better than 1 point of perseverance, and max strength of spirit.
-you should need more defense because you are focused hard in teamfights. Buy soul shroud, maybe rod of ages or stg. else.

Anyways, this is a very good dps build, but not really support build.

Fudge- I covered that in the items. I don't feel Sona needs it with her natural defenses (Heal, stun, speed boost), but, if you feel that way/are having problems, I list some options.

Tox- Alright then. :) I completely agree with you then, and will update to include that as an option.

Sona's passive, Power Chord's, counts as a separate source of Magic Damage rather than an on-hit effect, that's why it works on towers :P

great guide but a little more defense would be good cuz sona tends to get focused alot

Mmk. Thanks for the input guys. :) I've adjusted and updated based on your feedback.
Masteries-
The reason I had the points in the offense was for that cd reduction. But, by changing my masteries to max out Intelligence in Utility, I still have that same cd reduction. :)
I put the remaining points into defensive masteries, which I completely agree with you is far more useful. Especially early game.
I totally thought I had a point in Insight, but i've also adjusted the my masteries for that. I do think, however slight the amount of extra mana from expanded mind, it is more helpful than any of the other talents your could choose.
Items- As far as defensive items go, I find smart playing, as well as the massive amounts you can heal for late game (when you'd be getting those defensive items)plus your speedboost, mean that you don't really need it that much. However, I do point out (in red ;D ) that any survivability issues are easily solved with either a guardian angel or frozen heart.
The crystal scepter isn't a bad idea, however, except that I don't think it stacks with passive abilities. Correct me if i'm wrong, but i was under the impression it only stacked with activated abilities (Sona's Ult, Cait's net shot thing, etc), not passives.

Large wall of Text:

Your mastery tree..:
Perseverence - Why spend the extra 2 points on here? It increases your HP and Mana Regen by 4%, now if we look at the final stats on your build.. you get 60.13 Mana/5, Perserverence (1) would increase it to 61.33, level 3 would increase it to 62.54.. that means 14.52 more Mana in 1 minute (at level 18), which isn't even enough to cast any of your spells.. on top of that you're packing Clarity to remedy your Mana anyway. I'd suggest just to just leave this Mastery at level 1, the two extra points would have been better spent on other places.

Expanded Mind - Increasing your Max Mana by 5%.. according to your build, you get 2870 Mana (fully stacked Archangel's).. with Expanded Mind, you get 3014 Mana, which results in 90 AP from AA staff as opposed to 86 AP. Now if we look at the AP in terms of your spells:

Q / W / E / R
60 / 30 / 0 / 70
63 / 32 / 0 / 72

So you deal 6 more Magic Damage with Q (2 targets), heal 4 more HP (2 targets, including yourself), deal up to 10 more Magic Damage with your Ult (assuming they all get hit), and for Lich Bane, you deal 4 more Physical Damage... in the late-game. It -really- isn't worth the investment of 4 Mastery points, where you could have gotten Insight (Improved Clarity), Greed (1 gold/5), or Presence of the Master.

Insight - Since you plan to be a Support, why not have this recover more Mana for your lane partner as well? I'm personally not a fan of Clarity, but if you're getting it, you might as well get the improved version.

The Offense Tree - Instead of investing in the Offense tree and not getting Archaic Knowledge, why not invest in the Defense Tree? 8 Points in the Defense Tree could mean a small bit of Dodge to save you, early game Armor and Magic Resist, or even HP Regen (which scales with your Mana, which you get a lot of anyway)

Archaic Knowledge - Why not put a point in this? It provides 15% Magic Pen.. and since you planned on getting a Void Staff, it'd give a total of 49% Magic Pen (as opposed to 40%).


Runes:
I feel it's a bit squishy.. but I don't really have any problems with the Rune choices.

Items:
Why the Spell Vamp from Will of the Ancients? I can understand getting it for your team, but for yourself, it really doesn't recover enough to make it worth it (not enough damage to recover a substantial amount, and on top of that, Sona's Hymn of Valor and Crescendo are flagged as AoE spells, which means that the Spell Vamp is lowered for those spells, 25% -> 8.33% Spell Vamp on those.. though Power Chord still uses the full Spell Vamp, 25%).

Also why not get any Defensive items? Your Armor / Magic Resist aura would put you up to 90 Armor and 80 Magic Resist on 1710 HP, this equates to 3249 Effective Physical HP and 3078 Effective Magical HP. An Abyssal Scepter could be good for this build: It increases the Magic Damage done by your teammates (-20 MR for nearby enemy Champions), increases the damage that you deal (70 AP), and lastly it provides some defensive qualities (57 MR). Or perhaps Rylai's Crystal Scepter, despite her two damage spells being AoE, her Power Chord would slow for 35%, but Power Chord - Tempo would slow for a grand total of about 55-56% (as opposed to 40% from the normal Power Chord - Tempo).


I'm not saying anything bad about AP Sona, just some little pokes to make it better, that's all. Not bad a bad guide overall though, needs a little work but it's not bad.. colours :)

Quite interesting, Ima have to try this.
Never really played sona full AP/support
ususally I just build full support.
Anyways, pretty nice build

+1