Guinsoo's kog is extremely overrated and is not the most efficient build for Kog'maw
is bad because it's too hard to benefit from the max stacks, and it is a purely offensive item (does not offer lifesteal, mobility, etcetera).
In my opinion, the most efficient build is one which simply skips guinsoo's
This build is:
(sell
and buy
after guardian angel)

Runes are also important, I have found the best runes with this build to be: Primary Lethal tempo + triumph + legend: bloodline + coup de grace Secondary taste of blood + ravenous hunter
Runes are designed to get you out of early game with a lot of innate sustain, and lethal tempo helps you better scale hard into late game to compensate trading off damage for more defensive items.
were some of the things I'd see the most, but something shifted somewhere to make them want AD again.
style build on her over
where people try to use nothing but Lethality when Crit is still just as strong on her.
into