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I've done it mid a few times.
Mid is better suited for AD Malz as without Rylai's, you have no real kite and Malz has no escapes; mid is the shortest lane. Mid should also be getting the blue so you can have almost max CDR with blue, glacial shroud and offense masteries. I recommend not doing this in solo queue and rather making sure you have someone queue with you that's building some AP top lane or in the jungle. Many mids don't run armor so this is good. Top lane is dangerous to push most of the time--and as Malz you will be pushing--even with wards and especially without escapes.
Malz awesome at pushing towers and ulting things that are out of position. He's also strong at Dragon and Baron since the creep DPS is great. His teamfighting can be kind of derp since you're relying on your voidlings, but at the same time, the enemies are likely ignoring the pets.
I still think he works better built manatank rather than raw damage similar to say Yorick. The harder it is to kill you, the longer your minions get to eat away at things. I go boots + various pots to start. Get your tear as soon as possible. Your core build should be something like Manamune, choice boots, Glacial Shroud and Hexdrinker/Negatron. Then decide if you need to get a little tankier (Frozen Heart, FoN, Banshee's, Maw, Mallet are good options) or get your Last Whisper earlier.
AD Malz masteries require 14 in offense for dual penetration and the rest you can do whatever with. You could go more offense, defense or get buff duration and mana regen in utility. You can rune how you want really, but I'd recommend the AD/lvl marks and probably MS quints.
All and all, I think it's fun, but I wouldn't say it's terribly viable.