I wouldn't call AP items "offensive" on her, nor are her AP ratios aren't low. I wouldn't ever build Righteous Glory on her either.

Take note that an AP ratio of 0.8 (for example) on an offensive spell gets reduced by the target's resistance; healing does not work the same way. Either way, her self-heal has a ratio of 0.4 to 0.8, her heal has a ratio of 0.6 (on a 2 second cooldown), Equinox has two 0.4 ratios, and Wish potentially has a ratio of 0.8~. The only spell she has that has a bad ratio is Starcall (the damage portion of it).
I really fail to see how her ratios are low.

No idea why you seem to think stacking health on her is a good idea.

Ok first, I've greatly enjoyed you guide. I only have started playing soraka post 4.20. Mainly because I didn't like her old skill set. While here newer skill set is comprehensive and fun. My one main question for you is why no Ardent Senser (Sorry not good with links and ****, I'm old.)

Ardent Senser provides, Mana regen, AP CDR and makes all your heals/shields to allies cause increased Attk Speed. It's one of the new 4.20 items and for my Nami/Soraka its been on deck for a while. Thoughts

This build looks interesting and Zhonya's Hourglass is something that I've never thought about on new Soraka, I have to admit that :)

- Frost Queen's Claim is a good item for aggressive players, but I personally think talisman of ascension's stats are waaaaaaaay too awesome to ignore. It gives everything new Soraka wants; movement speed, mana regeneration, health regeneration, gold generation, its passive heals you and its active gives you and your allies more movement speed (you can never be caught with it and Boots of Swiftness).

- Spirit Visage is another awesome item for her, it's nice to have the same opinion about it :) I rush it after Boots, Sightstone and completing talisman of ascension, even if I'm against a full AD team (which is highly unlikely). Some people prefer Locket of the Iron Solari, yet self health regeneration is more important than your allies (yes, I'm selfish about it :p )

- Warmog's Armor is bad on her and worse now, since it's nerfed. Even if Warmog's health regeneration is kinda buffed, I still prefer Rylai's Crystal Scepter for half less health but more AP (which means more passive healing from Starcall) and slight slow.

I'm still experimenting so many builds on my main champion (and waifu) Soraka and your opinions are most welcomed :) My idea is that being as tanky as I can ( Spirit Visage, any desired armor item [new Ohmwrecker also looks interesting], Locket of the Iron Solari if jungler does not have it) while building less health, keeping my teammates alive as long as I can and also regenerating missing health like Dr. Mundo.

(I feel a bit lazy to talk about your runes, yet I think hp5 quints are more useful than flat health ones)

Great guide, well thought-out. I like the health-building option. It never occurred to me to do that. I will probably use elements of this in future builds.

Pretty sure you need guiding yourself. (Looking at the items at least)

In general, your guide is good. The runes are viable, the masteries are effective and the items you recommand are far from being bad. Final or not, there are perhaps some modifications that you could bring. The codes are not used properly, there is a lack of space between some texts making it looks heavy, the ideas that are not from you could simply be put in a bibliography: people tend to not read long notes. Over all, I like the practical aspect of your guide. Therefore, I don't like the esthetic of it.