Anchor Bolt Plans & Certification Letter. Duro Steel Buildings is well aware of this demand and offers the highest quality 100% recyclable steel buildings. Durobeam steel 60x64x20 metal building kits commercial prefab structures direct additional cost or not available. Our steel commercial buildings, with few width limitations, allow you to erect huge metal buildings with clear spans widths of 100 to 200+feet (30-60+ meters).