These are the ingrediants you will need to create your bag. (80 plastic bags,duck tape,cello tape,scissors,velcro/about 30 cm)

Step 1: Fold the carrier bag in half longways, and then half again,until you find yourself with a strip of bag.(make sure you do it neatly as this will make the following steps easier)   

Step 2: Using the scissors just snip off the excess handle from the bag.(as demonstrated in the picture.) 

Step 3: Take the strip and fold it over creating an L shape.(ensure you are folding towards you.)Take the same end and fold it behind on itself.Now with the longer strip of bag,fold that behind and around.You should have a small reverse L shape.You will notice that a pocket has been created.Tuck the flaps into the pocket creating a sqaure.     

Step 4: Make sure your square is as tight and as neat as possible.you can now take two squares and link them together as shown.Use a little tape on one side to join them together.You have now created one of of the complete squares.  

Step 5: You can now start putting the squares together to create a rectangle.you are going to need to make 2 rectangles.(4 squares high by 5 squares wide.)look at creating patterns from the squares.Once happy with your alignment,you will need to join the rectangle using celo tape.(Ensure you use the tape on the same side as before,as this will be the inside of the bag.)

Step6: Now carefully cut the duck tape to the length of the bag,and place over the seams where you have used celo tape to join the squares.Then continue to cover the rest of the surface with strips of duck tap,until you have neatly coverd one side of the bag.  

Step 7: Now place the two rectangles together side by side width ways.Carefully duck tape these together to create one solid shape that can fold down the middle.

This is the tricky part,you need to now take two pieces of duck tape,4 square long and stick them down from the middle to the top of the bag,so half the tape overlaps off the side.Now fold the overlaping tape back so the sticky sides up,and pull the the remainder of the shape over and on to the sticky side creating your bag.(as if you were folding a piece of paper in half and sealing the sides with double sided tape.

        Step 8. Take your velcro and run it along inside of your one remaining hole to create the opening of your laptop case as shown in the picture above.