Step 1: Materials List:
6 yards pinwale corduroy (45" w)
3 yards orange cotton (45" w)
9 yards white muslin (45"w)
double-sided iron-on hemming tape
Step 2: Measure Twice, Cut the Fabric, and Sew Borders
I'm going to call the orange bordered side Side A and the white bordered side Side B.
Because the center panels on my two sides had different internal measurements (that center panel), my orange borders (Side A) were narrower than my white ones (Side B). Side A is made of the corduroy and the orange cotton. I cut the corduroy into two 90" lengths and sewed them together along one side, forming a rectangle measuring 90" X 88". I cut the orange into four strips: two measured 7" X 90", and two measured 7" X 100". These measurements allow for seams. I sewed one 90" strip to the right side of the gray rectangle (right sides together, of course) and the other 90" strip to the left side of the gray rectangle. I sewed one 100" strip of the orange to the top of the orange/gray/orange piece and the other 100" strip of the orange to the bottom of the orange/gray/orange piece.
This formed Side A.
Side B, the panel and white border, has different measurements, because the internal panel is a single piece 45" X 56". I cut the white into 27" strips. Two were 56" long, and two were 100" long. I sewed the 56" strips to the outside edges of the graphic panel, and I sewed the 100" strips to the top and bottom of that central piece of white/panel/white.
Iron the seams toward the center piece (both sides of the comforter) and top stitch a half inch inside the center piece.
Step 3: Two Sides Together
Step 4: Finish the Open Edge
Step 5: Put the Comforter Inside
Step 6: Tips and Hints
Yes, you could do this with a single gigantic sheet. Well, two gigantic sheets. A California King will accommodate the dimensions for a King-size comforter.
Brace yourself: This is a LOT of fabric to work with. But it's just a matter of straight seams. If you're working with a great design or with colors you love, you'll see the project through.