Purchase enough muslin for the size of your banner, plus an extra eight inches in height. Remember that the banner will be viewed by an audience at a distance, so do a mock-up on cardboard or butcher paper to make sure the size you are planning will be seen.
Lay out the muslin on a surface you don't mind having painted and apply a base coat of paint to one full side of the fabric, starting at the center and working your way out to each side to stretch the fabric. Use a roller attached to a threaded pole, such as a push broom handle, so you can do this easily from a standing position. Most paint rollers have handles that accept standard pole threads. Use a 3/8-inch nap roller pad for a smooth coat. Allow the banner to fully dry, then paint the second side if you want a stiffer, more opaque banner.
Fold down the top and bottom four inches of muslin along the fabric's entire length and pin it into place. Sew along the two lines, leaving a half-inch beyond the seam. These are known as pockets.
Paint your banner as desired for your production, using the side opposite the seam as the banner's front. Chalk out lettering and designs before painting, or use an opaque projector if you want to trace designs directly from source material. Stage paints, available from theatrical supply stores, provide brighter colors than standard acrylic paints, but they must be diluted with water according to the constructions on the container. Use either stage paints or acrylic house paints for your design. Allow the paint to dry completely.
Add a grommet (a metal fastener similar to the eyelets shoelaces go through) to each end of the banner, according to your grommet kit's instructions, about half an inch from the top of the top pocket. Add an additional grommet approximately every four feet.
Insert one-inch OD (outer diameter) or smaller PVC pipe into both the top and bottom pockets, using PVC connectors to attach more than one length of pipe together if needed. These pipes will keep your banner hanging straight throughout the production. Chain can be used instead of pipe in the bottom pocket for a less rigid look.