They’re usually made from acrylic, polypropylene, or glass.
Widths commonly run from about 10 to 24 inches, depths around 4 to 6 inches, and heights roughly 2 to 4 inches.
Many include mounting hardware, anchors/screws/brackets, a wall-mounting paper template, hanging hardware, and note that adult assembly is required.
They typically use an iron frame, a wood frame, or engineered wood shelves.