When composing the panel, as well as the characters, I’ll also blueline in a basic perspectival grid and whatever props or features are required for the scene. Then I’ll assemble any reference required (mansion? mountain?) or make it up myself, sometimes in SketchUp as above, or with the pencil. I don’t usually spend more than an hour on a model; most of the details are filled in on the fly, while drawing. SketchUp is useful for avoiding figuring out complex geometry, yes, but also allows for consistency when revisiting a scene later. Because my work is analogue, I sometimes lightbox a printed-out model, and sometimes eyeball it from the computer screen.
I’ve never heard of preparing paper in either of these ways… or any other, actually. I just put a pencil on it and go.