Measure how long you want your curtains to be, from the ceiling to the floor of the stage. Add 8 inches to allow for your top and bottom hems. Measure the length of the stage and double that measurement for the width of your curtains.
Figure out how much fabric you need to purchase. Divide your length measurement by 3 to find out how many yards you need for each panel. Divide your width measurement by 60. Each panel will be 60 inches wide, since that is the width of most velour fabric.
Cut the fabric panels to the lengths you measured using scissors. Cut the number of panels you figured to go all the way across the stage.
Sew the panels of fabric together at the sides until you have the desired width to go across half of the stage. Repeat for the other half of the stage. This gives you an opening in the middle.
Fold the bottom of the curtains up 1 inch and fold again 1 inch. Use heavy pins to hold the fabric in place. Sew all the way across, removing the pins as you go, to form the bottom hem of the curtains.
Prepare the top of the curtains for grommets by folding the fabric down about 3 inches. Fold under 3 inches again. Hold the fabric in place with pins and sew all the way across.
Make chalk marks, evenly spaced about every 3 inches, all the way across the top of the curtain. One at a time, place a grommet on each mark. Hammer the grommet in place. When you've attached all the grommets, your curtains are ready for hanging.