This is not a build to be taken seriously by any means. I have not tried this in anything but a custom game. The only basis I have that this might be even slightly doable is that I solo'd Baron at level 17 with 2 Nashor's Tooth, Berserker's Greaves, Athene's Unholy Grail, and a Needlessly Large Rod... I was also rocking blue buff (had I not rushed Athene's and had blue, it would have not been doable at all) ended the fight with roughly 1/4 or 1/3 life, pretty sure my AP during fight was around 260.

I did Baron again at level 18 with full build with red/blue potions as well as red/blue buff. Did it in roughly 47 seconds (lots of mistakes made, probably could have shaved off 5+ seconds) But, when I had killed him, I was at full health- AP for fight, 595.

It's pretty much the same as AD/Jungle/any other Xin role. Use your W/E, then pop your Q to lower the cool down of those. With this build, since you have such high CDR, literally you can keep your W up next to constantly, and your E can be used about every 2 seconds.

Also, do not be afraid to use your ultimate, with Q spamming your cool down is pretty low on it. Any time you find yourself in the middle of a team and getting focused, E onto their squishiest AP/AD carry, ulti, then auto attack. You'll heal up nicely before the melee even have time to run back to you.

Keep in mind, this is just theory on how you can play him for right now. I will work on this guide more as I have time, and I'm going to play AP Xin more when I have the chance. This is literally just something I thought up while bored at work today and figured I'd test it out in a custom game when I go home. It worked surprisingly well, so here's this guide so others can try for themselves.