Exterior, Cabin Building Type, Wood Siding Material, Metal Siding Material, and Flat RoofLine For the Butterfly cabin, which is part of the Post Ranch Inn, Muennig chose materials that age gracefully when exposed to the elements. He regularly uses Cor-Ten steel, a group of steel alloys that form a stable rust-like appearance when battered by wind and rain.  Photo 72 of 101 in 101 Best Modern Cabins from Big Sur: Coastal Commissions