Alright, I don't normally post that much on the forums, but since i saw one with malzahar i thought i'd put my build. Malz is my second char i ever bought and I play him when I feel like doing well.
Normally start with Doran's Ring, although if I feel like I need to get into my build right away I get Boots. Then I go mid and in 5v5 my first skill is E, since it can help you push your creep wave early on, assuming the other team isn't psycho for ganking, and you can out-level your opponent, score more gold, and regain some mana for your kills.
Then I wait until i have 1600 gold before I buy anything, then I buy the Large Rod, the early AP is rather beneficial. After that I usually buy Boots of Lucidity so I can maximize cooldowns, because if you have all of your spells and full mana you rarely die 1v1, and with runes and masteries you should have about 15 flat MP, then get 15% magic pen, and that usually gets me through a game, and if they start stacking MR, then I buy absyl scepter which has 20 flat MP.
After boots i get a hat, and then start building towards Morello's so that I can maximize how many spells you cast a game. And it's always a good feeling to have your ult ready in case that one enemy gets a little too close. After those three items, [Boots of Lucidity, The Hate, and Morello's] you can really get whatever you want, 9 times out of 10 i'll build for another hat, but most of the time the games don't last that long. After that is really up to you, if you're using a lot of mana then get Archangel's Staff after your first 3 items to help with max mana and mana regen. As for your sixth item I honestly don't know, because I never really reach that point in the game where i can buy a 6th item. If you want a little more movement speed you could get Lynch Bane, but honestly I'd rather just get another hat, just because I like landing a nice Q then throwing my ult and watch their health disappear.
Now haters are gonna hate, and I know the way I play probably isn't the best for everyone, but I like to spend money on wards if ganking is getting bad, but other than that I really stay back a lot, let my team mate initiate then provide support from afar. It really leaves a lot up to team mates and sometimes you get the cheap KS, but then again, malz shouldn't be up on the front lines anyway.
But the decision is up to you, I'll tell you what though, I sure didn't find my build looking at all the other ones, it depends heavily on your style of play and your opponents. Hence why some builds work well for some games, and completely suck at others.