Speaking of tissues, have you ever been troubled by the ugliness of Kleenex boxes? (no offense to Kleenex!) I always try to buy the most neutral looking designed box. There really aren't any cute ones to choose from! Here's another solution:
First, measure your tissue box. My box measured 9 inches wide, 4 inches tall, and 5.75 inches deep. Here's the best drawing you've ever seen:
Add one inch for seam allowance. Before you cut out your pieces, add one inch to each measurement to allow for a 1/4 inch seam on all sides.
Cut your pieces. Cut two "face" pieces 10" x 4", two "side" pieces 5" x 6.75", and one "top" piece 10" x 6.75"
Hem the bottom edge of each face and side piece.
Attach the face pieces to the top piece. With right sides together, sew each face piece to the long edge of top piece. **Start and stop your seam 1/4 from each edge.** When finished, press seam allowances toward the top piece.
Cut out the center hole in the top piece. Place your sewn portion wrong side up on top of your tissue box. With a pencil or other marking tool, trace around the box opening.
Cut out the opening 1/4 inch inside of your traced line. Cut a small diagonal slit in each corner. Press the flaps toward the wrong side of the fabric. Top stitch around the opening to keep the flaps in place and to give it a finished look.
Attach the side pieces. This part is a bit tricky. Sew the first side edge to one of the face pieces by lining up the hemmed edges. Stop your seam 1/4 from the end of the side piece. With your needle down and presser foot up, line up the next edge of the side piece with the edge of the top piece. Again, stop your seam 1/4 inch from the edge and line up the last edge of the side piece with the final face piece. Follow these steps to attach the second side piece. Trim corners if necessary. Finish off by pressing each seam crisp to give your cover a nice boxy shape.