You should get a roa by min 18 even if you buy boots first, usually my case. but sure, RoA can go before.
The thing with revolver (and especially wota) is, it`s really a secretly OP item for Ryze, it gives 25% spellvamp, imagine a double wota scenario, thats 50% vamp ALL THE TIME, this is specifically op for Ryze because he can cast to infinity unlike most mages, his ult doesn`t last forever, double wota does, his ult is something you need to save for his long rotation (qeqwqrqeqwq in case you`re wondering), you shouldn`t relly on it for healing only, if you use the ult too early your dps will greatly decrease, with double wota and ult you get a character that has high health, damage, defenses and 75% spellvamp, thats just absurd, you should try it out someday, you`ll be amazed.
3.9k HP, 180 armor,
4.1k mana, 337 ap, and if i`m lucky 50% consistent spellvamp.
Q is the strongest in a way that you should be able to spam it a lot, if you read his passive you`ll notice that every spell he cast decreases all of his cooldown by 1, the point of Ryze is that you use Q, then another spell in hopes that Q is ready again, repeat to infinity
Your priority when leveling spells should be R>Q>W>E