which ryze is better? full AP or full mana?

i like using ryze, he's my favorite champ. i am currently in bronze tier, and in one of my games someone told me i need to go flat AP in order for ryze to do damage. i had frozen heart, building tear, and was working on RoA. This person was telling me I needed to buy liandry's, deathcap, and zhonyas. since i'm in bronze, i can understand why this person thinks that way. i do the average ryze build. Seph, RoA, FH, Sorcs, void staff, and my last item really depends on the enemy team. most of the time i use my last slot on visage.

has anyone ever tried a flat ap ryze? does it work? btw if my build is not correct, i don't mind constructive criticism. also pointers would be great.

again, my build is 1-Seph 2-Roa 3- Sorcs shoes 4 Frozen heart 5 void staff 6 Spirit visage, another RoA, thornmail, iceborn, banshee's, book of the ancients. (this really depends on enemy team)