Generally speaking its ROA asap and then... what? whats some good damage items on him. since he gets so much cdr from his ult i want to shy away from frozen heart bc most of its cdr is wasted due to the passive 30% that ryze gets at 16
I'm no Ryze expert; probably it will take a while for people to really figure out what's best, but I've played him on PBE a bit. Generally you want Tear ASAP, then RoA. You want to finish your Archangel's/Seraph's once you know you'll fully stack your tear before your next back. For a third item (outside of boots, which I generally take Sorc boots or a defensive boot like Mercs or Tabi depending on my needs), I think Righteous Glory is very strong on him, since it gives him more mana and health, but also the MS active which helps him get in range and stick to targets to get his full combos off. You probably want a Void staff, as you do with most AP carries, and maybe something like Zhonyas since your AP ratios are improved, but also new Ryze is less able to build tanky than old Ryze, so the Zhonyas active is really nice.
I've also seen some people get Muramana, since his E procs it multiple times if you attack someone in a minion wave, so it absolutely will destroy a target in the right situation (and will also cost like 1k mana on it's own). It's kind of crazy though, so I wouldn't be surprised if Riot removes that interaction in an upcoming patch.
In general, his starting build should remain the same, tear into RoA into finish AA's. You just don't have to throw in any CDR anymore.
After that I guess you can build tanky offensive-defensive items (with stuff like Righteous glory, Zhonya's, Rylai's, and Abyssal scepter, or even straight up defensive items) or just build offensive stuff like deathcap, luden's echo and void staff. Or an even mix.
Potentially there's some really cool stuff you can do with Muramana and stuff. But sadly Frozen heart and Iceborn Gauntlet are no longer really buildable on him because you automatically overbuild CDR (unless you don't get any offensive masteries).
There's also stuff like gunblade for more spellvamp I guess.
Tear>RoA just like before, but instead of FH, you'll want to build him more AP heavy now (they nerfed his mana ratios considerably while buffing his AP ratios). Basically, Ryze has to build like a tanky mage now, not just a pure tank with lots of mana.
I would suggest going 9-0-21, getting 10% CDR in masteries, and get hybrid pen marks, flat/scaling health or mana regen seals, AP per level glyphs, and flat AP quints, and then build 
. With this setup, you'll deal a lot of Burst and DPS and all your spells will have minimum cooldowns, while still being pretty durable.
and three situation items to reach the right level of defense, movespeed, and the ability to not go OOM. As long as you stay in range, don't die, and are not OOM you will do plenty of damage. The only exception is if there is someone that must be deleted ASAP every team fight and there is no one else that can do so, in which case turn to the usual suspects for any AP scaling champion that build out of 
.
As a note, gives more damage after slightly more than 200 AP (including death cap) than 
does per spell rotation.
