Mikhail do this, neccessary items are the ones you build first, always, then, if you need more of a certain thing, ive put them in categories. Remember to buy in components, not full items.

pick facets accordingly

Red dragon is an all rounder, Does both physical and magic damage, pick if youre feeling indecisive

Green dragon is for melting armor, and does only physical damage, so against tanky heroes is good

Blue dragon is antiheal, against heroes that rely on their health regen, IE Necrophos, Slark or Huskar