To make a tissue box cover pattern, draw the front and side of the box to scale on a piece of paper. Draw half of the box top, splitting it down the center along the tissue opening. Add 3/4 inch around the exterior of each piece for a seam allowance, and cut out the final patterns. Write "cut two of fabric and two of interfacing" on each pattern piece as a reminder.
To complete your tissue box cover pattern, add instructions for assembly. Cut out two pieces of fabric and two pieces of interfacing using each of your pieces. Iron the interfacing on to the back of each fabric piece, and lay the top pieces together to form the top of the box cover. Fold under the center-facing edges by 1/2 inch, and sew along the folds.
Sew the front, back and side pieces together with the right sides facing in. Use a 1/2-inch seam allowance. Sew the two halves of the cover's top to the top edges of the sides, ensuring that the folded edges face the center to form an opening for tissues. Flip the cover inside out so the right sides of the fabric face out. Fold under the bottom edges by 1/2 inch, and sew around the fold.