So I came up with this idea, it may not be very revolutionary but it could easily be adapted to other products and I am going to make another version for my Nintendo DS at some point.
Firstly I wanted to keep everything really simple so I created a rectangular pattern I decided how far up the laptop the opening would be and how far down the flap would come. Make it a little wider that the laptop itself. See pic.
This photo shows how high up the laptop and the section above is the flap which will come almost down the the base of the case.
Before I got too carried away with the quilting I added two magnetic fastenings.
These are easy to use but you do need to take care when making the holes to insert the prongs on the back of the fastening.
Make two dots where you would like the top and bottom of the fastening to be. The back of the fastening has a split pin so make small holes either side of the position dot. (Sorry about this photo, looked much better on the camera!).
Here I have both halves of the fastening ready to snap together. If you are concerned about magnets and your laotop then use another form of fastening.
Using Bias Binding
Sew the binding onto the back of the fabric. I used to do this the other way around until a friend showed me this way. Put the pins at right angles as this makes them easier to pull out.I then stitched along the edge of the binding with the machine foot next to the edge of the fabric.
Turn the fabric over and carefully bring the binding around to the front and pin again. Try to keep it as straight as possible. You may need to trim some of the fabric if the binding struggling to go over the edge. Then stitch along the edge of the binding to secure.
Fold your cover where you had decided to have the flap etc and again using your bias binding seal the side seams. Remember to fold over the raw ends of the binding to prevent fraying. Use plenty of pins at this stage to stop the fabric from moving too much as you stitch through all of the layers of fabric.
*Add a strap