Drill holes in one side of your wood block, making them 3 1/2 inches deep. Make sure you do not drill all the way through, but leave about a half-inch of wood at the back of the holes. Make as many holes as you want.
Attach the thin piece of wood or shingle to the top of the house as a roof. Make sure the back of the roof lines up with the back of the wood block and the front overhangs the front of the block. Nail two of the nails into the roof piece at either end in the center so as not to nail through any of the holes you drilled.
Nail two nails on either side of the block of wood in the center, leaving half an inch hanging out.
Attach string to both nails. The string will loop easily around a post or fence top.