This pillowcase can be customized to fit the size of your pillow once its done.
The width should be the same for all.
The inside cover and big cuff should be cut at 12 1/2 inches.

Image credit: SewVeryEasy on Youtube
you’re free to cut the decorative band between 2 and 2 1/2 inches.
For the back, the same width plus 36 inches.
You start with your front cuff, big trim, and front piece.

Start by making the front of the pillow.
So the pillow is right-side up.
Take the band and fold it in half so that the wrong sides are touching.

And the raw seam is going to match along the edge of the pillow fabric.
Take the cuff fabric and have the right side facing down.
Match your seams and put in about 4 or 5 pins.
After temporarily pinning it, you flip it over.
Take the edge of the fabric and fold it right in the center of the big cuff.
Fold it again and again.
Take the floral design cloth right over to the edge.
Match up the edges and re-pin.
Straight stitch a quarter inch all the way down the edge.
Then take out the pins and pull the insides right side out.
The pillow front is going to come loose.
You will have no exposed seams on the front or back.
Its time to work on the back of the pillowcase.
You have 2 pieces of fabric left over.
The back, which is 36 inches, and the inside cuff, which is 12 1/2 inches.
Take one edge and do a rolled seam.
Doing a rolled seam is simple.
You just roll the fabric once and press it.
Then turn it a second time and press it.
Stitch right along that fold.
Lay the larger back piece with the good side facing up.
Then take the inside cuff fabric and place it on the back piece facing down.
Then stitch a quarter inch on the edge.
Fold the fabric and use the seam allowance as a guide.
So your pillow case is now done.
So if your pillow back and front are done, all you better do is sew them together.
Lay the pillow back out with the right sides facing up.
Match up the front so both good sides are facing together.
Use the folded line to be the guide for your fold.
Stitch the sides with a zigzag stitch.
Do this on all three edges.
Dont stitch the top part.
Then take the blue flap and pull it towards the back.
When you pull it, you see a trim.
You just have to stitch right along it.
And your pillow is done with a flap.