MB3 108a: Ladders, Palm Branches and Stones on Shabbos (308:18-21)

A ladder normally used to plaster the roof or another melacha is muktzah. Palm branches cut down for use as firewood are muktzah. Placing a non-muktzah item on top of a muktzah item. Designating an item for use on Shabbos (e.g. a block of wood for sitting).