Jellicle cat costumes were used in the Broadway musical "Cats" to great effect. Despite their lofty pedigree, these costumes are pretty easy to make. You can use a jogging suit or find a pattern at a craft store.
Purchase a stretchy fabric. Lycra or jersey are both good choices. For colors, stay in the silver, brown or burnt orange range. A unitard could be used--they're available at most dance supply stores--but it won't hold color.
Make the arms of the costume by crocheting or knitting sleeves in half lengths, to reach from wrist to elbow. Cover them in fur and then slide them onto the lower half of the arms over the bodysuit.
Create legs that partially cover the feet by either crocheting or knitting leggings. Cover them in fur as well. They should reach to the knees. You can use craft paints in cat-like colors to add stripes or spots.
Pack a pair of pantyhose with newspaper to make the tail and glue pieces of fur it. You can attach it to the bodysuit by sewing, or use a safety pin, super glue or even Velcro. See the related eHow article "How to Make a Wearable Tail" for all the steps.
Fashion the headpiece by sewing a hood directly onto the bodysuit and add the fur and ears. Make a fluffy mane around the head so you will get the Jellicle cat look. The fur can match the costume color or be a shade lighter.
Complete your costume by adding the finishing touches with makeup. Accentuate the eyes by painting cat-eye lines all the way out to the edge of the face and adding whiskers. Now you have the purr-fect Jellicle cat outfit.