The Difference Between EXTERNAL FROM IS. That is whose stars shoup be Made of Material that is not Subject to Dampness, Rotting. In the Snow and Frosty Season, The Steps of the Stars Shoup Not Slip, Its Easy To Clean from the Snow. Most Offen, Brick, Concrete, As Metal Structures, Natural Stone Or Combined Materials Arewktafacture of Extranal Stairs. Wood for these Cases Short -Lved Material.