I'm the Riki that KingKaslob was referring to, Riki is my dude.
My build for him varies depending on the situation, but early on I get poor man's shield, magic wand, power treads, diffusal blade, then yasha. If I need to be more durable I can get a morbid mask in there somewhere, and later upgrade it into either vlad or mask of madness (most of the time I don't get a mask at all). The yasha is then upgraded into either manta style if I want to max dps, or sange+yasha if I need more health. I also upgrade diffusal to level 2 when I run out of charges, diffusal's active is amazing. At this point, I get butterfly, and once I have that, the game is over, if it isn't already.