To create the costume, wear blue jeans or blue jean overalls -- the older, the better. A worn shirt, again an old, worn shirt is best. A plaid or flannel shirt is common. Some people use a piece of fabric as a mask -- brown or tan loose weave old-fashioned bag cloth is good. This cloth should look like one that you'd use to hold straw for a scarecrow's head. Paint a face on the cloth or draw one on with permanent or fabric markers. Instead of a cloth or mask, you can also use facepaint -- a dark nose and bright red circles on cheeks are one option. Use some stuffing to make the clothes fit in a lumpy way. Adorn with bits of long grass or straw and old string.
Other options include a stick like the ones used to hold a scarecrow up in a field or a stuffed bird on a shoulder. Another shirt option is a bulky, old sweatshirt.
One usage of this costume is for lightheartedly spooking would-be trick-or-treaters: The individual in costume will sit on the porch near the door in the costume, not moving until trick-or-treaters come up, and at that point will move suddenly and usually make a loud noise.
- Wikipedia's article on scarecrow
- How to Make a Scarecrow - about how to make scarecrows rather than human costumes, but has lots of pictures and may help with ideas