Clean the inside of a one gallon milk jug using dish soap and water. Turn it upside down, with the lid off and leave it to dry overnight.
Use a utility knife to make a hole in the side of the milk carton. If the milk carton has a circular divot on one side, use this as the guide to cut the hole. Cut around the edge of the circle and discard the cutout. If the carton does not have a divot, draw a circle that is approximately 2 to 3 inches in diameter and then cut it out.
Tie a 24 inch piece of twine to the neck of the milk jug, just below where the lid attaches. Tie the twine to a tree to hang the birdhouse.
Clean the inside of a metal coffee can using dish soap and water. Clean the lid as well. Dry the can completely.
Use a drill to make two pilot holes in one side of the can. Place one hole 1-1/2 inches in from the bottom of the can and the second hole 1-1/2 inches in from the top of the can in a parallel line. Twist an eye screw into each hole and tie a 12 inch piece of twine through each screw. If you do not have eye screws on hand, feed a 36 inch piece of twine through the holes and tie the loose ends together.
Use a utility knife to make a circular hole in the coffee can lid. The hole should be approximately 3/4 inches above the edge of the lid and measure 2 inches in diameter.
Replace the lid on the can so that the hole is down and the eye screws are up. Use the twine to hang the completed can from a tree.