Sorry, I didn't make myself clear! Yes, I mean a pouch with some depth, with a zip over the top half and a gusset round the bottom. I'm not explaining myself very well but I want it to look like a hamburger once it's sewn, with a zip over ther top.
OK, that is clearer....Think (but in much smaler scale) a round pillow with a zipper inserted into the gusset.
Basicly, you need two circles of fabric the size you desire (you can use a can or plate as a template) + 1/2 inch for a seam allowance
A strip of fabric as wide as you want the gusset + 1 inch (1/2 inch seam allowance on both sides) by 1/2 the distance around your circles + 1 inch (1/2 inch seam allowance on both ends) (call this gusset A)
A strip of fabric the width of the gusset + 2 inches (this will provide you with 1/2 inch seam allowances) by 1/2 the distance around your circles + 1 inch (1/2 inch seam allowance on both ends). Cut this in half _lengthwise_. This will be for the zipper. You will also need a zipper at least as long as this strip is long (it can be longer). (call this gusset B)
You will then sew the zipper to the two halves of gusset B by aligning the edge of the zipper to the long edge of one strip (right sides together), stitching close to the zipper teeth, then pressing the strip to the side of the zipper and top stitching in place. Repeat for the other side. Close the zipper and tack the ends of the fabric together, making sure the zipper pull is free to open and close the zipper.
Stitch the short ends of gusset A to gusset B, creating a loop. Stitch this to the circles of fabric (right sides to right sides), trim and clip seam allowance, turn and press. You now have a cirgular bag with a zipper.
To line, simply repeat with lining fabric (except you will not be stitching the zipper into place, leave that part open), insert it into your bag, turn the raw edges under and whip stitch the opening to the zipper opening.
If you want to add a strap, stitch it into the seams when you sew the gusset ends together. You can also add small pull tabs in the same manner.
I hope this is clear enough for you to follow. If you try it, let me know how it works. I am flying "blind" as I am writing directions from memory, not as I sew.