It is simple and easy to do it. I did go a bit wrong with the zipper as I was trying out this different way to attach it. But in the end it turned out to be pretty fine.
I have also tried to keep the inside stitches clean by first stitching the three closed sides right-way out. Next I pulled the inside out and ran a stitch all along the three sides with right sides in. This way the inside stitches do not show the rugged edges and besides it also adds strength to the stitch.
I will soon come up with a tutorial for this as I find a DIY cushion cover to be far more better than a store bought one.