Roa is what gives you most of your power and survivability in early laning. It helps you stay in lane much longer (Cataltst of the Protector), big ap boost (Blasting Wand) and a stacking increase of HP MP and AP over time (Passive) reducing the need to immediately buy more ap to do more damage. You say, "well the reason i dont like rod is that it just gives hp and mana", well you DEFINATELY need the mana as you eat it up early game ridiculously fast (if you are playing offensively) and the HP boosts your survivability during chases and from nuke ults.

This allows you to immediately jump into movement speed, ap damage, or other things that offensively increase Ahri without having to worry about more survivability until later in game, when which I do buy Ryali's Crystal Scepter. I just think that early game you don't need the slow that badly, as you wont be chasing someone for long periods of time until you get a lot of mana and so-forth. On my guide I go more in depth into that, feel free to look.

well the reason i dont like rod is that it just gives hp and mana ..yes the catylyst affect is nice but not worth buying the rod just for that.

the thing is that with out resistances hp dosnt do u a whole lot of good and the only reason i like to take the giants belt first while building the crystal scepter is to give u a little wiggle room inbetween casts and spellvamps.

and the crystal septer is more for the slow. the fox fires count as single target hits so the crystal scepter wil get it's full slow on the person and u will have an easier time kiting

but like i been saying it is really wat ever works for u i personally dont like building hp on her for the sole pirpose of building hp because i know i wont build any resitances

plus the tear goes to the archangels which is nice for the amoutn of ap and mana it gives and can be stacked to replace the majei's if it isnt working out well

first, rod of ages is cheaper than rylai's.
second, RoA gives more HP AND MP than rylai's.
as you get mana pool from RoA, you don't really need tears of the goddess.
besides, rylai's gives 15% snare (and only 15) with all Ahri's spells except charm (35%).
you can still get rylai's later if you really want more HP.

as you don't use swiftness, you don't have movement speed until you're damaged.
you also don't have the 18 + 5% AP bonus from offense mastery.
but using defense mastery can be interesting.
I gonna test and I'll come back for my impressions.