Too much AS, drop zerks for sorcs and drop nashors for a tank AP item. Kogmaw is so innately fast and hurricane is so powerful you are sitting near 2.0 attacks a second with only malady and hurricane.
EDIT: also be aware that any iteration of ap koggles is an absolute mana pig. Unless you are planning on building full on hit, which means you should be considering different items entirely. Consider tear and later manamune as an investment or at least come up with some way to mitigate his mana costs
EDIT2: did some mathcraffting and based based on hitting a decently tanky target with 2500 health and an even 100/100 in armor and MR a your best bet is going to be muramana, liandry's, void staff, malady, hurricane and sorcs. It does something like 890 raw DPS to the primary target and 730 raw to each secondary. Adjusted damage is something like 635 dps primary, 555 DPS to secondaries. You will be blowing through mana like no ones business and you will not be happy if someone says hello up close and personal, but with a powerful poke and near on 1800 DPS across the enemy team no one should care.
Now if you swap the muramana for an AA/Seraphs, your magic damage actually stays about the same with the toggle on but it gives you more defensive options and staying power, it also boosts your E and Q higher. Though due to AD sacling on your ulti you round off pretty even in terms ulti damage.
Here is the thing though. Between your Q, and malady, which I did not include you should be close to true damage on anyone that looks at you funny. It takes about 2 seconds to kill a carry. Less if you consider the fact that your powerful Mpen allows you to chunk them with spells for more than a thousand damage. (true damage on MR below appx 125, hyper true damage on any fool who has less than 50 MR, QE combo is 750 damage, each subsequent R is 440, with a good 800 sustained DPS waiting when they step into range. Note that muramana procs on q and can add to 120 extra damage.)