You choose poorly by waiting to get Radiance. Tarics Ult is one of the few that allow for longer lane presence and extended pushing. The items are nice, but they need some work. I understand this is an AP build, but you need some survival itmes. Things like Rod of Ages, Rylai's Crystal Scepter, hell, even Haunting Guiese. All give you AP, and give you like too.

Ive built a Nuke Taric, its on my profile, but you built a glass cannon. He will nuke, but be nuked. 2K life on a tank, even if he is AP, is just sad. I dont see how you last in 1v2 lanes, or team fights. Im sorry, but with that amount of life, Taric is just too squishy