at the beginning i'd go for: Cour, Wards, 3x branchen, tango, clarity.
after this i feal that shadow shaman is a great drum carryer, as it helps him to close up to the enemy very early on to get off his hex/shackle. in addition with a magic wand, you should be finde to go for the blinkdagger directly.
you can go forcestaff as a next item, but i feel blinkdagger is a far better item for SS, as it gives your team to punish every enemy that is only slightly out of position. even though id go for aghanims after blinkdagger, as the upgraded ultimate gives you a great tool to break enemy bases.