Non-standard cages — i.e., metal returnable containers — are common storage vessels; note two points before purchase. First, stability. Stability of non-standard cages has long been a key issue in warehouse steel-structure design, and widespread structural use makes stability research urgent. Uncertainty runs through design, manufacturing, and use; reliability analysis before non-standard work is needed rather than guessing dimensions. Second, fit your own warehouse. Plan the warehouse yourself first, or have the maker's technicians build to fit. Utilization then climbs, and future failure odds drop. Have working conditions, cargo weight, stacking layers, and rack spacing ready before talking to the maker — the plan comes right in one pass instead of back-and-forth revisions.