Thanks for your comments!
I got the pattern from a book by Terence Terry. I'll post the pattern and the directions on how to do it. You'll need corrugated plastic board for the bottom. You can use cardboard too, but I wouldn't advise it, since cardboard gets funky when it gets wet.
1.) Use the pattern to cut out the pieces of fabric for the main bag, adding an extra 1" for the seams. Cut out the iron-on interfacing for all pieces using the same pattern.
2.) Using an open-ended zip, pin and tack it onto the right side of the zip panel (but now you should have cut the zip panel along the cutting line). Maching along the stitch line and trim the seam allowance. Fold over to the right side. Repeat for the other side of the zip. Zip the two pieces together.
3.) Place the pattern for the zip panel centrally over the sip and mark the new seam lines.
4.) Keeping the ride sides of the fabric together, stitch the two "bag sides" (the one under the zip panel on the pattern above) to the end sections of the zip panel. Trim the seam allowance and press.
5.) To make the handles, cut some leather cord in half (I couldn't find leather cord, so I used rubber tubing and inserted rope in it to make it sturdy). But the ends diagonally.
6.) Fold the fabric handles down along the edges. Wrap around the leather cord, and using a double thread, whip stitch the two folded edges together.
7.) THIS IS WHERE THE BAG COMES TOGETHER: Place the handles on the side panels of the bag (wherever you want them to be). Tack them into place. With the right sides and maching notches together, tack and stitch the main body of the bag to the zip panel/side bag (what you stitched at step 4). Avoid sewing over the leather cord, since that could ruin your machine...instead, sew diagonally where you cut the cord. *This step is such a bitch to do...I had to do it like, three times each side because the curving parts were so hard to stitch.
8.) using your base pattern, cut a piece of corrugated plastic card 1/4" smaller than the original pattern. Place the card onto the fabric for the base.
9.) Tack a piece of lining on top of the card. Using a piping foot (I used a zipper foot), stich around all sides as close to the card as possible.
10.) Your bag should still be inside out (wrong side facing out). Stitch the base onto the base of the main bag. MAKE SURE THE ZIPPER IS OPEN, OR ELSE YOU WON'T BE ABLE TO TURN YOUR BAG INSIDE OUT!
11.) Using the pattern, cut out the lining pieces. Now, stitch it the same way you stitched the bag, starting with the zip panel. What I did was I folded them in, so it gives a neat finish.
12.) Now, turn the lining inside out. Here's the annoying part: you have to turn the main bag inside out. It's SUCH A STRUGGLE but hang in there!!! Then place the lining into the bag and slip stitch the top to the zipper.
I hope this helps...