This project can completely change the look of your room with out investing on a new comforter or quilt, as well as protecting you quilt or comforter.
These fabric requirements do not take in to consideration matching prints. You will need more fabric which will depend on the repeat of the print. For example: If you are making a twin size duvet cover using 45" wide fabric, the fabric requirement is 2 times the length of the cover. If your repeat is large, you may need 3 to 4 times the length in order to match the prints at the seams.
Small prints such as calico fabric should not require matching. I always buy extra fabric, to add complimenting trim to curtains and pillows.
You will also need to repeat your top fashion fabric or use a sheet (same as the bed size you are making) for the bottom of the Duvet Cover.
Closures are a matter of choice. For these direction I will be using 3/4" buttons and button holes. I have also seen zippers and Velcro used to close duvet covers.