Sorry for double post, but pictures would be nice. Too much of a text block now...

You lack too much mana regen, Clarity can't cover that much. Either pick mana regen runes instead of armor runes or buy simply more mana regen. That much will never be enough even with Clarity which has a cooldown or you're not taking most advantage of her passive and aura dancing. Not enough cooldown reduction either, maybe build a Shurelya's to cover mana regen AND cooldown reduction? Or simply Morello's Evil Tome.

Also about runes, maybe you want full HP quints, I don't see the need for one mag pen quint especially since you build Abyssal Scepter. Maybe you wanna consider a team that doesnt have many casters so in case you won't really need Abyssal scepter, then suggest to build something else? Maybe then that Shurelya's or Morello.

All together the idea seems quite nice, but you shouldnt need that much defense, becausae as a Sona you need to position yourself behind everyone pretty much out of reach. Nice idea though but it's better to get more mana regen and cooldown reduction to make most use of your skills.

Runes: Hmm, I would prefer Armor seals on her instead of Health, and give her full Heatlh Quients instead...

Items: Because Sona's mana dependent, I'm surprised you're not running Tear, and building that into AAS, as it will give her more AP. I'm also surprised you would suggest will of the ancients as she already has a self-heal (her heal will heal a nearby ally and herself).

-edit

Never mind, after some contemplation I can see where you're going with this guide. I was pretty slow on the uptake.

Well since ppl rate and don't comment here i go.
I run sona since lvl 10 or so don't take it personally.

I can see the point of the build as a faceroll caster with support items.

It will work but its nothing new.

Its a reliable build if y have a good team composition, but if y go for solo QUe will probably get blame for all the **** in the world.

Tell you what show me some screens of some scores...

and ill rate y afterwards.

P.S: How many times y get rabadon.