Why does the bible refer to "God" as Elohim when "Elohim" is plural for "gods"? And in Genesis the verse that talks about two types of water and the expanse: what is this? - Dion
Elohim is plural, but so are the cities Sardis and Colosse. There may be a faint echo of a remnant from polytheistic times, but this is by no means clear. Plural though it may be, Elohim is used in a singular way.
About the cosmology of the ancient world, I would refer you to the recommended reading at the main website: Books > Recommended. Then search by category. Short answer: until 500 years ago, much of the world believed that there were waters, or even an ocean, above the firmament. For more on this, see my book Compelling Evidence for God and the Bible (2010).