Alright, a forewarning to everyone: This is my first tutorial and is going to be super mecha choppy, so be flexible and DON'T BE AFRAID TO E-MAIL/IM ME! Also, when I actually make purses, I make it up as I go along, so if you're confused, take a stab at it a few times and make it up! It'll be even more unique^^ That goes for measurements/exact details. Everything is relative.
Here's what we're trying to achieve:

Here goes...
First off I would suggest using a heavier fabric for the outside or base fabric, much more resiliant and all that. I've used 2 types of heavy corduroys in the two I've done.
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1. The Sides
Cut out a the shapes of the sides, which will depend in size with your personal preferences. A big 'U' shape crossed with a banana and a semi circle will about explain it. Mine ended up being about 30 inches along the bottom edge. Tip: I've found that its better to have them less-banana like and in a deeper' U' (unlike this example), it makes them slouchier in a better way.

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2. Other Pieces
Cut out the strap and bottom of the bag pieces, the strap should be just about as big as the measurement of the bottom curve of the side, and the bottom about 2/3 that big. (ex: bottom curve = 33 in. so strap = 33 in. and bottom = 22 in. ) But that all depends on how gathered you want the base edge in the final product, its all you my friend. Also cut out pieces from your chosen lining to match ALL of your outer pieces, yes, they all need a lining, even the strap.

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3. Pretti-fy it damnit
At this point, any decals or adornments (patch-wise) that you want on the front of the bag should be applied/sewn on, so that you don't have to do it when its all gathered and such.

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4. El Strap.
Now its time for the strap. Technically you could do it at any point you'd like, but I'm going to throw it in now. Alright, you have your long piece of fabric to use for your strap, and in my design, I have an hourglass shape to it and some accent fabric (usually some of the lining material) inside the shape. The picture is pretty self explanatory for the first part.

To get the fabric inside, just use the piece of lining you cut to the lenght of the strap piece and trim it down so it fits under the over lapped outside material, and sew along the edge of the under flap first, then the top flap. From the other side you should get something resembling a big swooping x with a circle where the lines cross. I'd use a zig zag stitch so that you don't have to fold under the edges of the flaps (hence the heavy fabric= no fraying)

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5. The Zipper.
Lay the zipper along the top curve of one of the side, good side of zipper to good side of fabric and sew along the edge, joining the two. the zipper will have some 'pooching' in it, but that just goes without saying. Next, lay the lining (good side down) over both the zipper and the side, the zipper separating the tops of the two pieces of fabric, and sew that as well. If you flip the side and liner so they line up , you'll have a clean edge on both sides of the zipper.

Repeat with the other side. When completle, if you lay it all out, you'll look like you have a big fabric pancake. Yum.

Sew the linings to the edges, bad sides together (thats the only way you can do it at this point ((hopefully....)))

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6. The Gathered Edge
Along the bottom curves, use a very large stitch to sew 2 gathering points on one side of the 'bag' thusfar. I used 2 because I kept breaking the string having to gather that much thick fabric on such a little thread.

CAREFULLY gather the bottom edge until its the same length as the bottom piece. (If you haven't, sew the lining to the botom piece) Sew the gathered edge to one side of the bottom piece, good sides together. Its going to be curvy and bumpy but such is life. Just go with it and if it looks wrongish its probably right, its a strange looking deal going together.

Heres an example of what mine looked like (or a section of it)

Repeat that whole dealio with the other size, and MAKE SURE YOU HAVE THE ZIPPER OPEN WHEN YOU SEW THE OTHER SIDE!! An inside out purse is nooo good.
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7. Alright, heres a crappy drawing of what you should have. Yours is going to have much more rumpling, and probably won't look exactly like this in its perfection (rolls eyes) So don't worry dolls.

Alright. Now for the handle, which is the toughest part to explain (but the easiest to do...) Picture first though, it'll help me out.
http://img.photobucket.com/albums/v365/black_rabbit13/experiment/14.jpgAlright, with all the zippers I've used, they've been old or slightly damaged, so I've never had too many problems getting the handle through that funky little hole which you have at the end. So I really have to just say make it up, I think you'll get the gist though, you have the bag inside out (zipper open) and have the handle inside and slip the ends through those holes and sew the whole end together. MAKE SURE!!! The side of the strap that you want facing out to the world is going to be facing out, hold it inside with your fingers, pull part of the bag back rightside out and check it out.
*******What I like to do when I'm pretty much done is use a zigzag stitch and go over all of the rough edges/seams to try and stop them from fraying a little bit.
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AND YOU'RE DONE!!!!!!!!!
Thanks for breezing through, and please please PLEASE!!! Feel free to mail me and ask questions!! LIke i said, its my first tutorial and i'm pretty much winging it^^