You might wanna switch out your glyphs for scaling AP as they begin to surpass flat AP around level 6 or 7. I would rather max my CDR, but if getting focused is never a problem for you, I guess the soul stealer would do. Over all the build is not bad, but I think that it could be optimized. Also, recommending that people try a build against bots is kind of silly.

The #1 zilean guide doesn't build mana at all! I never find myself starving late game. He has built in cooldown reduction that i can spam late game for ult and my boots give CDR... please read before just -1 because you have a guide.

Oh hay! You made a Zilean build too, awesome. Not enough mana, you will be starving for most of the game, You have NO cooldown reduction at all which makes your ult slow as hell lategame, and you build full ap lol. It sucks, -1 from me