Very Thin Wire

At the scale of the building, a thin wire, stretched taught enough, is a close approximation to a line segment.

Again, this is a matter of scale. The wire is likely to be thicker than a line drawn by a pencil. On your desk the wire is too thick to be considered a line segment. Perhaps a thin, straight pencil line is thin enough to be considered a geometrical line. If that is too thick, then a length of spider silk stretched between two points might work.

But on an architectural level, taught wires can be considered line segments. You could build a geometrical model of the building using line segments to represent edges. such