1st build: remove CoA, uselessness at its finest, put one point in amplified curse and get CoEx (maybe improve it 4/4)
drain life isn't so imba to be worth improving, as we're talking about maybe 40hp per cast? most of the time you'll be full with siphon life+draintanking
I'd go for CoEx and suppression instead
why?
well, let's kill a creep in a contested area..
*CHEAP SHOT*
amplify curse>coex>siphon life>corruption>pet on rogue=dead rogue
deathcoil if needed, altho it didn't exist when i was leveling so I'm pretty sure you can live without it