Well I since Malzahar is free I seem to see alot of malzahars failing or not carrying hard.
Even with a malz that was a better player then myself I won because of my items. So I would just post my build and runes!
This "guide" is for someone who already played him and to discuss items/runes
I will not type 5pages about skills because I presume the readers to already know how to play him on a basic level!

Malzahar has great farm and harass power! this combo lets him dominate his lane early game and make him scary even late!

Some remarks on items:
Rushing spellvamp: being low on hp makes you vulnurable for ganks or having to go back!
If you cannot afford spellvamp in one buy get boots first and some pots, the sepperate items for revolver are useless.

Sorcer's shoes: Magicpen is never bad: with boots and runes together I have 30magic pen flat enough to do full damage to a squichy character or support

why no tear?: Through his dot (E) mana shouldn't be an issue in lane, outside lane or before teamfights blue could be usefull, but with runes I can usually deliver the pain until the end of the fight!

Deathcap: a must for all AP casters

Rylai's Crystal Scepter: By now they will realize not focussing you will lose them the fight-> so getting hp is a must, the slow and ap are such a great plus that missing this is impossible!

Now you got the core build finished
The remaining items are dependend for each game who threatens you the most?
Magic => Banshee's Veil / AD => Glacial shroud

Still playing? sell the "Hextech Revolver" and get one of the last items:
More then 80 Magic Resist? Void Staff
AP damage: Abyssal Scepter
AD damage: Zhonya's Hourglass

I only have 1 remark here: Null-Zone

This spell is very mana consuming so spare it for when teamfights start or you got ult up and want to ensure a kill!

If you got a towerhugger against you then I don't level it up until E is maxed out!
more damage = more mana back = more farm = more cash
Do not ever farm with it unless you need it to defend a tower!
The rest is the basic sequence that every experianced malz player should take!

Some guides suggest more mana > more experience, I think we all know that hitting lvl 6 asap is alot more important!

Only character that may do that is ryze because mana = damage for him

The basic stuff

ignite during ult will not interrupt it
Alternatives (over ignite : never go without flash) are ofcourse: Teleport
Lesser spells you could take but shoudln't be needed: Clarity - Exhaust - Ghost

Here I'm not a 100% sure mine is the best, but worth discussing:

I got 10magic pen so withboots I nullify them early game
Flat AP is great for farming and keeps me in lane until I prefer to go shop

Charging up your passive at Fountain is a must, don't forget if you need to pull blue then only 2casts are needed!

The first lvl's just last hit (malz got a good range and hits quit hard for a caster)
and wait until lvl 3 thne the dot should be strong enough to farm an entire wave with just one spell

Catapult/Canon minions are a ***** and will stop the dot from jumping (or you have massive AP) try hitting them with Q/A

Alright I know how squichy you'll be the first lvl's so against a high cc team their will be better builds, but still I use this item path to great effect!

Keeping the enemy pushed at tower gives me great farm and chances to go and gank!

Also sorry that the guide doesn't look great, but I just did this after a discussion with an other malzahar where he didn't understand my item choices!