Always open:
2x tangos
4x branches
1x ring of protection
Side-shop or courier(mid) the sobi mask asap, bottle first if you need to but most likely you won't need it.
Phase boots, bottle when you run out of regen and need it, then there are essentially two core builds which are dependent on what you're facing and if you're the only carry.
If you're facing any sort of melee carry your orb will be skadi, if you have to hard carry you'll want satanic, general items will be mkb+lifesteal/skadi+manta.
Purge is useful against things that need to be purged or mana-burned and in it's current state it's pretty imbalanced but not really necessary.