Some simple ideas for children's costumes from parenting.com that can be made by yourself include a bubble bath, a weather reporter, and a raining cats and dogs costume. For adults, a lady bug and a big kid are popular ideas.
According to Parenting.com, raining cats and dogs is as simple as putting black felt cat and dog cut outs on a clear umbrella and then using the child's own raincoat and rain boots. This site also recommends a weather reporter costume by using a card board box covered in burlap, a large helium balloon and some science toys if desired. The parenting.com website also suggests the bubble bath costume by using an inflatable baby bathtub, ribbon and white balloons.
The adult lady bug costume is made with a red dress and black felt circles. A headband made of black pom poms and pipe cleaners is an easy addition according to the website. For adult men and women, a big kid costume is very simple as the only item needed is a pair of pajamas according to popsugar.com. To add some character and authenticity to the big kid costume, carry a stuffed animal like a teddy bear and wear little or no make-up.