I read everywhere that junipers ahould be outside. But should i cover it or bring it inside if it's raining?
They must be there where they are in nature: outside.
Do NOT bring it inside.
If you use proper draining soil, in general, no cover is needed.
Imagine a juniper in nature - there are no junipers that use umbrella's and still they are doing just fine.
It's not a puppy.... it's a tree.