Here's a trick for 'saving' wallpapers and other 'Materials' you may want to try out.
Use the wall draw feature to create a wall outside your floorplan. Drop a door on it, then narrow it to it's smallest (to minimize space). Make multiple copies of the door and spread them across your wall stub. When you scrolling through the materials sections (wallpaper, stone, wood, tile, etc.) and find a pattern you want to save to try out, drop it on a door.
This will 'save' the patterns in your "Room Materials" tab. By putting them on doors (rather than just little wall sections) this prevents them from being erased if you use the "decorate all walls" icon. hth :)