Rage blade gives 30AD 40AP at first, total of 54 AD, 72AP, and 64%AS when fully stacked.
This is extremely stat efficient and basically first build on Kog ADC. Something I want to explore though, is an AP scaling on hit build, rather than a flat one. Since Rageblade is already a good start for an AP/AS build.
Nashor's tooth offers 50% AS, 80AP 20% CDR, and 15 + 15%AP on hit damage. If we combined this with the on hit damage from rage blade, we would have 35 + 15% bonus AD + 22.5% AP to the primary target. that's 35 + 8 + 34 = 77 magic damage on hit with just those two items. Which combined offer over 114% AS.
This might be hard to Justify given the alternative of BotRK, which offers 60 damage for every 1k current health. But one of the reasons I'm looking in this direction is because of Kog'maws other AP ratio's, both on his Bio Arcane barrage as well as his ult. I also look in this direction because if I can focus mostly on the magic damage. (From items, and passively from Bio Arcane Barrage) I can more easily build penetration with items like Wit's end, or possibly even void staff.