1) Since my bags are just an excuse to do some machine embroidery, I made the front panel than added fabric to the panel so that I had a rectangle the same length and height as the top of a normal shopping bag.
That is a rectangle about 40 cm by 80 cm of main colour ( including panel) and lining the same size too. Then join the seams to make a tube.
2) To make the bottom, cut a rectangle about 30 cm by 18 cm .You need to position this rectangle so that the long edges are along the front and back, with the sides of the bag coming from the shorter edge of the bottom rectangle piece.
What I do is determine front and back centre and match that to the centre of the bottom long edges. Stitch those front and back seams first. Then do the two (shorter)side seams of the bottom.
Cheat : If you have trouble getting it to fit, its ok to do a few tucks on the bottomside seams as long as you do the same to both sides. You can also make the corners a bit fuller to take in extra fabric.
3) Now to make the shoulder strap or straps.
What I do cut 2 pieces of fabric the length of the strap ( about 120 cm for adult) and about 7 cm wide, out of the lining and main colour.
Then with right side together, sew along one edge, turn and top stitch, as shown.
Then turn in the raw edges about 1 cm on the other side and top stitch so you get a neat strap.
4) I then position the lining inside the bag with wrong sides togther. I use either contrast or main fabric to make the top edge. This means making another strip about 7 cm wide and the length of the top edge (80 cm). Join short seam to make another tube.
Stitch it to the top edge by going right sides together with the lining, then turn and top stitch so you have a neat finish on the top. You should start at the back so the join isn't so noticeable.
Then position the strap ends and top stitch the strap on the bag ends with a square and cross, as shown.
Here are the latest three bags using a fairy . I asked for their favorite colours and used that to guide the colours in the fabric and embroidery.
This is a great way of showing of your embroidry or smaller crazy patchwork and quilting efforts.
here is a close up of the emroidery panel
materials: main fabric and lining : 80 cm x 40 plus strap 122 x 7cm and top trim 7cm x 80cm