A clear and simplified commencement of Sona. The format is fine but you ought to include chapters "Pros/Cons" & Summoner Spells higher up the list. For whatever reason the picture in the Warding section isn't showing for me.

Runes

I'd include Greater Seal of Armor for these wanting to boost their defensive stats to become more resilient and to be able to come on top of trades with the enemy AD carry especially after Hymn of Valor early ranks nerf.

Masteries

Actually 0/9/21 is the standard support build. Sage makes very little difference and Perseverance is practically unnoticeable mid or late-game along with no harm being done taking a point out of Awareness . Allowing you to also pick up Durability & Veteran's Scars making you more tough so you aren't as squishy when landing that perfect Crescendo or being among the radius damage within team-fights when spamming Aria of Perseverance to keep up fellow team mates.

Items

If you need to spam your spells then either the AD range carry or yourself are doing something wrong. You shouldn't really have any mana problems with: Philosopher's Stone, Expanded Mind , Meditation and if any mana problems did occur they will be long gone late-game. So there isn't really any need to get Tear of the Goddess, getting it also sets you back in items and coincidentally that means losing gold since you won't be able to get your GP5 items as quick.

I'd include Randuin's Omen in optional items as it is vasts uses in that its on use active cripples the enemy AD dealers as well as severely undermining the effectiveness of AD carries particularly these of which that synergies with attack speed such as Vayne with her Silver Bolts. Along with many other positives in making her more durable, CDR and a great passive. I'd go a step further with Vision Ward against these certain champions in getting Oracles Elixir, an item that accounts for its own context.

Sona AP ratios are atrociously poor making buys like Archangel's Staff & Morello's Evil Tome rather ineffective for "pushing the advantage" so to speak. Getting Will of the Ancients would provide more team utility and AP that would be of more value to others.

Summoner Spells

I'll expand on the description of Flash giving citation of its aggressive use for instance Flash > Crescendo.

Pros / Cons

I'd include how shes one of the most mobile supports with Song of Celerity (second only to Janna).

If I could, neutral would be my vote. Guide and Build have some errors. Try to organizate your topics better, for example, you should talk about pros and cons in the start instead of in the end topics. Also, the guide is a bit incomplete. You should talk further more about Clairovoyance use, warding and gameplay style.