I tend to spoil myself and use the wide backing fabric which is usually 108" wide so no seams, but normally you would piece for a queen size quilt. You can choose just one fabric and piece a couple drops together to get the width and length you need or you can piece it with different fabrics for interest or include left over blocks or...well you get the picture. I know some use sheets for these large backs, I prefer not to for various reasons but it is an option.