Storm, the white-haired mutant of African descent who can control the weather and suffers from claustrophobia, is one of the most enduring members of the X-Men. Popularized in pop culture by Halle Berry in the film "Franchise," Storm is a very recognizable superhero and serves as a great basis for a costume.
Storm's most prominent feature is her white (or sometimes silvery) hair, so that's a must for any costume. If you have a white wig, your work is done; otherwise, you can look for white or silver hair highlights at a large drug store or a salon. Wear your hair as messy as possible; as someone who's constantly making wind blow, Storm rarely looks as though her hair is combed.
Throughout the comics, TV shows, and movies, Storm has always been portrayed a bit differently, so you have some creative license in creating your costume. In general, there's a white version, used by the comics and cartoons, and a black version, used by the movies.
If you want to look like Halle Berry from the movies, you'll have to find skin-tight black clothes, preferably leather. If anybody you know owns a motorcycle, now would be a good time to ask them if they own anything you could use. Black boots, black leather gloves and a black sheet to use as a cape complete the outfit. If you can't find anything the right color, consider spray paint.
For the comic book look, deck yourself from neck to toe in white, accented with a yellow belt. Also invest in a simple white sheet to use as a cape. If you have black electrical tape, tape one stripe down each arm and each leg.
The X-Men Badge
What really sells the costume is one of the easiest parts: the X-Men badge. It's a circle with an "X" inside; the outline of the circle and the "X" are colored black, while the background is colored red. Create it with construction paper or markers, and pin or tape one to your shirt collar and one to your belt.