I know that Hybrid Kog Maw is far better than the full AP one, but though, this build is more like an alternative. Most of the hybrid Kog get immediatly focused because of their huge DPS, this build can do some nice damages too, and you will always get away safely. Truth to be told, this build is more focused on scores like 7/0/X than on 23/5/X.

Last but not least, this build is not over at all :). I will add some pictures soon, to explain how to play him efficiently.

I agree with Dalacman, hybrid or AD is more powerful on Kog due to the extremely low AP ratio on Bio-Arcane Barrage. I tend to build Kog as more straight AS, though, since that's what the Barrage scales best with, and then a touch hybrid instead of worrying too much about itemizing for a lot of AD or AP.

As a separate issue, I'm not sure why you take a point of Swiftness over Improved Recall . .5% move speed is only a buff of 1.875 movement, which is almost nothing. 1 second off your recall time is certainly much better, as it will save your life.

I understand AP Kog'maw looks like a good idea, but hybrid or straight AD is so much better. The ratio for damage on Living Artillery stacks so much better with AD items. You're also completely ignoring Madred's Blood Razor, the definitive item for Kog'maw. If you replaced Wit's end with Madred's and put Malady earlier in the build, you might be doing some serious damage with Bio-Arcane Barrage and not denying Kog'maw one of his best damage outputs.