This is a quick and easy method from the book 'Winning Stitches' by Elsie Campbell:
1. Pre-wash and iron fabric. Fold in half across the length of the fabric, lining up the selvage edges.
2. Stitch a 1/2 inch seam along each lengthwise edge. If the selvage marks are wider than 1/2", stitch a wider seam.
3. Trim the seams to 1/4", trimming off the selvages.
4. Cut across the fold and press the side seams open.
5. Re-fold the tube of fabric so that the seams lay on top of each other, and cut along one side. Open up the backing.
Four yards = 144 inches, but you only need 126 total inches (55+4+4x2), so you could cut 1/2 yard off the 4 yd before you begin constructing the back. Keep in mind that with this method, the two side panels will be going the opposite direction of the middle panel, which would be obvious with a directional fabric.