this is how you played ryze pre-change, his AP scaling isnt good anymore. Build ryze as a tank/support or go home. he gets enough AP from his ult unless they are stacking MR which is not likely in the current metagame.
Not entirely true. Ryze AP ratios are actually excellent. Overload isn't so great, but that's because it scales off mana too. Rune prison and flux are both good. That said, ryze is squishy as hell and you will provide much more team utility and damage building tanky with CDR than building burst AP.
Not getting one rank of spell flux is also just wrong. Not only will that nerf the hell out of your team utility, overall damage, and farming, it is also almost certainly more burst damage to have one rank in spell flux and -1 rank in overload. I don't have the #s in front of me for his abilities, but not even counting the -MR it's gotta be close.
My personal build is 1 in each ability, then max Ult > Prison > Overload > Flux.
Start with doran's ring. Get Catalyst, Deathfire, BV and go from there depending on enemy team comp (boots of choice, I get mobility). Deathfire lets ryze gib almost anyone from 100% to 0 in one spell rotation.