This is the time when you need to finish off the game. These items varies from different situation and scenario.
by this time, mobility is very important for shaman inorder to gank and roam the entire map. purchasing a blink dagger is very crucial at this point of the game. Aghanims will also enhance Shamans ultimate skill which is good for pushing.
at this stage, mana is very important to you and your teammates who are mana dependent, make sure to get the arcane and the aether lens for added mana regen and cast range which is useleful for shamans skills.
at the start of the game, wards and courier are important purchase for a pos5 shaman.Just the basic items for supports