A multi-tier storage systems is generally constructed using standard pallet racking and shelving components.  Shelving is constructed in the same manner, however the racks frames will be 5m+ high to accomodate atleast 2 levels. This height can be increased by however much available head room there is in your warehouse allowing approx 2.5m per level.  Walkway aisles are between 900-1200mm to allow mobility when retrieving or picking stored products.