Chu's Maokai is still wtfbbqhax to me. His item build is a cluster**** of **** that shouldn't work at all, but somehow manages to work for him. That being said, I wouldn't recommend that if you're not Chu because it doesn't make any goddamn sense,

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I've always been of the opinion that you should open as a caster with Maokai and transition quickly to tank, a la Bryden7's Malphite. Open with a 2-3 dring stack and then transition to Sunfire + MRes item of choice (Abyssal, Fon, and Banshee's are all good). I also feel that I chug mana like a boss with Mao and have been considering switching the dring stack to 1 dring + chalice of harmony OR philotone + chalice, but I don't play a ton of him anymore so I can't comment on whether that's actually a smart idea (not to mention I usually like to have only 1 big ticket mres item and feel short on mres a lot). From there I would grab either a deathcap (vs. low mres teams, where I would usually get abyssal for Mres as well) or a void staff (vs. tankier teams), but the truth of the matter is that if you just need to keep tanking, you can get away with just building more tanking items.
Now, if you really feel the need to do a lot of ****, I'd say the best way to itemize CDR on Mao would be to open Philo/Dring -> Chalice -> Spirit Visage -> Frozen Heart (akin to many WW builds ATM). Visage helps his passive and the whole package gives you 30% CDR, good tankiness and the mana you'll need to keep casting your **** as it comes off CD. The biggest issue here is that you have no offensive investment, which shouldn't be that big a deal because Mao's base damages are relatively high and has relatively average AP ratios. After finishing that core you could grab a RoA or Deathcap or Voidstaff or Abyssal or w/e for offensive output. You can also do this build with a RoA rush to start, but in that case ditch the chalice since you'll be getting such a big mana pool from your items.
Boots should usually be mercs, but sorc shoes can give you a lot of early lane dominance vs. squishier characters.
For runes, I used to run flat AP quints, MPen marks, Armor seals, and MRes glyphs. I don't like CDR runes except for a few on Vlad to make yourself hit 40%.