Buy approx 50-70cm of each (112cm 0r 150cm wide) fabric, one colour for the outer, and one as a liner. I like to use quilters cottons as the range of colours/patterns is much nicer, but any non-stretch fabric would do. The plastic can be found in the tablewear section of stores like Spotlight and Textile Traders and costs around $6 or $7 a metre. Sometimes its hard to get hold of so if you are planning in making a few bags it pays to buy up big when you see it in stock somwhere.
The general idea for cutting out is to cut a large rectangle and then cut out identical sized squares from each corner. The size of the square determines the depth of the bag. For my example above, the overall rectangle was 52 cm X42 cm and the little squares that got cut out were 11cm x 11cm. Sewing with a 1cm seam allowance this resulted in a finished bag with the dimesions of 30cm wide, 30cm tall and 20cm deep.
Once you have worked out the desired dimensions cut 2 of the lining, 2 of the outer fabric and 2 of plastic. The handles are should be about 8 to 10cm wide. The length can vary depending on if you want to sling the bag over your shoulder or not. 60-80 cm if you want a shoulder bag or 50cm if you want them to be carry handles. Cut 2 handles from fabric (I like to use the same fabric as the outer bag fabric) and 2 from plastic.
Sewing the lining...
Place the pieces of lining fabric right sides together and sew the left, right and bottom seams. NOT the little square cut outs.
NOTE... if you want pockets on the inside of you bag you should attach those to the lining before you begin sewing it together.
Crappy photo I know, but on one of the side seams leave an opening of about 20cm- this is because in a later step you will need to turn the bag right side out. Dont be tempted to make the hole smaller than 20cm, the plastic is hard to get through anything smaller.
This is a tricky part to describe. The little sqaure cut outs are now pulled apart so that the botton and side seams can meet. Sew the seam to create the corner of the bag. I hope the picture helps you understand what I wrote. I am not even sure that it makes sense!
Thats it for the lining.... now you need to make the outer shell, the handles and then join them all together.
Sewing the outer shell...
Lay one of the outer fabrics face side up, then lay the two pieces of plastic on top of the fabric (see pic above). Finally lay the second piece of outer fabric FACE DOWN onto the plastic. As you are doing this ensure there is no fluff/thread/dirt sandwhiched between the fabric and the plastic.
If there is it will stay there for ever and mock you every time you use the bag. I speak from experience. The fabric slides easily on the plastic but you do not want to pierce the plastic with pins so instead use bobby pins to hold the layers together.
Sew the outer shell together the same way you consutructed the lining, but ommit the 20cm hole in the side seam. Sewing with the plastic is fiddly as the fabric slides on it and the plastic sticks to itself. Take your time, you want to avoind unpicking mistakes as this leaves holes in the plastic.
Sewing the handles...
Lay the plastic on a flat surface, fold it in half and press it to create a crease then unfold. Place the handle fabric on top FACE DOWN. Fold the edges of the fabric/plastic to the centre. The crease you just made serves as a guide. Use Bobby pins to hold the folded edges in place.
Now flip one of the folds onto the other, so the edges of the plastic is now hidden inside the handle. Bobby pin in place and topstitch the edge
Topstitching the other edges finishes the handle off nicely.
Make two identical handles.
Constructing the bag...
With the outershell wrong side out, position the handles in their desired locations (one on each side) and hold them in place with bobbypins. Turn the lining so that it is right side out and place it inside the bag.
The right side of the lining will be touching the plastic of the outer shell and the handles sandwhiched between the lining and plastic. Match up the side seams of both the outershell and the lining and Bobby pin all the layers together.
Sew around the top edge of the bag to stitch all the layers together.
Pull the lining out. See the little hole you made in the lining? You need to fold/scrunch up the outer shell and push it through the hole.
Just like this!
Gently unfold and tease out the plastic. Your bag is almost finished..
Stitch shut the hole in the lining.
Topstitch around the top edge of the bag to stop the lining wanting to roll outwards. The machine foot likes to stick to the plastic, so you need to pull the fabric through from behind.
Ta Da!!!! Now go shopping in a nice little cosmopolitan grocers store and enjoy all the comments as you load up your bag with organic vegies.