and also, consider things like void staff and BV, as bigfatlp suggested

I wouldnt really get ghost and exhaust for malz. I would rather take ignite and flash, but i guess you have decent reasoning for it.....

Oh and flash makes it easier to hit your ult. flash in for a gank, drop the pool, ult their face off.

Malz is mostly a nuker with a couple poke abilities and relies on hia ult suppress to get people caught in his pool. i think DFG would be a good choice because (correct me if im wrong) you can use its active during your ult and it gives 60 ap, 10 Mp5 and, 15% cdr. Also i know this for sure you can use ignite during your ult. i think if you are planing on getting RoA rush it you want the additions ASAP. this would allow you more staying power at all points in the game (sorry you wont be hitting as hard, but you should be doing more sustained Dmg, my comparison your build is like annie while the additions i have mad in this comment make you more like brand [still nukey, but not as much]).

Thank you both for your feedback. Trojan, what is your reasoning on flash being essential on malzahar? And the banshee's veil makes sense to me, thanks for putting that out there, but if i was to use it what should be replaced? I'm finding it hard to find room for an item like that in this type of build. Thanks for the constructive criticism. Cleru, you make valid points with the cdr and mana issues, do you think roa instead or rylai's would solve the mana issue? Or do you think that rylai's passive is too valuable to give up? And im going to try out the zhonya's hourglass and see how i like it, if it work's better i may change the build. Thank you both for your comments.

You really need more survivability in the build. like wahwah said a Zhonya's hourglass could possibly replace the 2nd rabadons or the abyssal scepter. Its just a matter of fact that in games with high elo you will get focused without some sort of protection you will die and all your AP stacking will be pointless. Another thing is that you don't have any mana or CDR items on Malz. You will oom out of all fights because of your low mana. You can get blue but it will never always be up. His Cool Downs are another thing a Malzahar without ult is only half as strong as a Malz with ult. All champions need a balance. In your case your AP stacking will offset on how well you do when you are under fire or being focused. Survivability > or = Nuking is extremely necessary in all levels of play.
Edit - Build is viable with a CC heavy team that is able to pin down the enemy will you wait for CD so I will vote up.

-1 for two significant reasons:

1. no flash. flash is ESSENTIAL on malzahar.
2. no banshee's veil. BV makes it so malz can actually cast a full-length ultimate.

Also, Please play with the build before commenting or voting. Don't just base your comments or votes on what you assume.

thanks for the feedback wahwah, ill try that out. I disagree with the guy above you though. Thanks for your feedback as well.

i dont like deathcap stacking. i think hourglass would be better, it give tons of ap and some armor + the AWESOME active. In a teamfight, run in destroy the carry pop hourglass, survive, burst to win. because the second deathcap isnt worth the 3600 gold because the passive is unique.

bad runes. bad build order. nice description though