What are you going to BE?
What a wonderful question. You can be anything that you want to be (providing of course that your mom will make the costume with you, or that they have it for sale at the TG&Y)
This last Halloween my daughter (for reasons only understood by her) decided to be a Mime. The sign made the costume work. In the past we have made Crayons, Fortune Tellers, A Giant Squid (way too much work, and WAY too heavy for the kid), Jessie the Cowgirl, Harry Potter, Pac Man and many MANY more.
The key is… be creative, make it fun. If you love to sew or craft, go for it! If the thought of surrounding yourself with glue and fabric makes you sweat, buy the costume.