Originally Posted by Malah
Also, I hear that Khazix is tanky and totally hard to kill.
This is sort of the problem, actually. Yes, you can build him glass, and he will work like Rengar, but worse... OR, you can build him like an AD version of Kassadin, and he will be nearly as strong as Kass (without the hard CC). He has great base damage and great ratios, so you don't lose out on much by building him with Armor Penetration, CDR, and durability.
Edit: When I say, "great" I actually mean, "pretty stupid OP."