Liberal scholars typically think Gen 1:14 refers to a vault or solid dome. Suppose we grant, for the sake of argument, that the narrator is using an architectural term connoting a roof or ceiling. Let's compare that to Exod 14:22, where God divides the Red Sea. The narrator describes a "wall" of water on either side of the Israelites, as they walk along the (temporarily) dry seabed. That's an architectural term for the defensive walls of fortified cities. But, of course, the narrator didn't think this was a solid wall, made of stone. He's using an architectural metaphor to describe the appearance and function of the phenomenon. Since the Pentateuch is a literary unit, it would make sense for the narrator (the same narrator) to use an architectural metaphor to describe the appearance and function of the sky. It's a hermeneutical virtue to have consistent principles of interpretation.