A shelf apparatus for use with a ladder or scaffold structure is provided. The shelf apparatus includes a substantially planar shelf structure having a plurality of holes positioned on a first side, wherein at least one of the plurality of holes is formed about a first axis positioned substantially perpendicular to the shelf structure. A cross-member engagement support is positioned on a second side of the shelf structure, the second side of the shelf structure opposite the first side, wherein the cross-member engagement support is formed about a second axis running from a first edge to a second edge of the shelf structure, and wherein the second axis intersects the first axis. A ladder-attachment structure is affixed to the shelf structure.