How can I temporarily cover up a bathroom door to a shower room?
You could try installing two expandable shower rods across the doorway. One should be shoulder high the other knee high. Mount some hooks on to a sheet of plywood. Hang the plywood on the shower rods by the hooks. Or just hang a shower curtain on the rod and place a do not enter sign in front of the entrance. This method may keep you out of trouble with the local fire department as blocking an entrance/exit is generally frowned upon.