What are things that are compared to the sky? The only element I can think of is ceiling, or dome, so I am wondering if there's any other word aside those two that can be used as a metaphor for the sky.
Is this what you're looking for?
Some of these are synonyms more than metaphors, but I'm not sure that isn't what you might be looking for. The metaphors are buried in the examples given. Let me know and I can tailor it more.
- Heavens/celestial realm
- cloud-lands/realm of giants
- the blue (or blue yonder)
- the land of the ancestors/gods
- bird-home/aviary of the gods
- the sea of stars,
- the roof of the world,
- the breath of life/God
Here is a page with some metaphors for cloudy/rainy sky if those are helpful.