The Malzahar build I use is nearly OP. The only thing that makes it not OP is the cost. It WILL take you the entire game to farm, and 7/10 times you won't complete it before the end. This build is very very powerful and will enable you to carry your team as Malzahar and not die, as long as you play smart.
Start with Meki+hp pots for Vision spam (Vision mana return+meki mana/regen is very powerful...most offensive start there is, imo)
Upgrade Meki to Tear of the Goddess
Farm for Blasting Wand and NLR
Make a Deathcap and Archangels
Get Boots of Lucidity when Move Speed and CDR becomes necessary (I get it following hat and angels)
THEN choose the following in whatever order you deem necessary:
This build gives you +HP, +Armor, +Magic Resist. As well as a lot of AP. At the end, you will be around 700-800 AP, 2300-2500 hp, 80-110 armor/magic resist. In the likely event you don't complete it, after angels and hat, you will be at around 375 AP, which is still really good. So you will still be really strong with even a partial build.
If, for any reason you don't need armor or magic resist, substitute the item for a Void Staff, which will provide greater net DPS than either item. Good luck, happy hunting.
I use CDR glyphs and quints to offset the lack of CDR on the items. I get 3% CDR from masteries, 15% Magic Pen from masteries, Magic Pen marks, and flat Mana/Regen seals. You won't need scaling Mana/Regen seals since your mana regen is already through the roof with Visions. That's also the reason I use CDR boots. With the new changes to CDR values, you will be at about 33% CDR at lvl18. The 7% off cap will not make a difference, because you will be hitting them so hard.