First of all, I'm using a sturdy canvas fabric (from IKEA) so that I don't need to bother with interfacing to strengthen the material. I suggest reading through the entire tutorial before getting started.
Print out the pattern, piecing it together matching up the labeled cross-hairs (pattern pages will slightly overlap). Place the pattern on the fold of your fabric and cut one piece from your outer fabric and one piece from a coordinating liner fabric. You'll also need a rectangle for the inner pockets measuring about 30" x 8". And you'll need a strip measuring 8" x 2" for the closure ribbon.
Now to prepare the pockets... If you have a serger, serge the long edge of the pocket piece that you would like to become the top of the pocket, then fold the edge in about an inch and press. If you don't have access to a serger, just fold the edge over twice to enclose the raw edge. Then topstitch to hold the edge in place.
Now take your liner fabric and mark a line on the right side about 3 inches from the base (the mark will be covered by the pocket).
Then line up the long, raw edge of the pocket along the underside of the line, with right sides together. I'm pretty sure that'll only make sense after looking at the photo below.
Pin and sew about 1/4 inch from the edge of the raw pocket edge.
Then fold the pocket up against the liner fabric and press along the fold. Then topstitch just over 1/4 inch from the fold, to enclose that raw edge.
Now your liner fabric should look like this:
Use chalk to mark lines where you would like pockets. (I usually make about four or five large pockets and one narrow pocket to hold a pen or pencil.)
Now fold the liner piece in half with right sides facing each other. Sew the side seam with about 1/2" seam allowance. Repeat for the outer piece. Now fold the pieces as in the picture below and press the seams open.
Now sew the bottom of the outer fabric, leaving a 1/2" seam allowance. When you sew the bottom of the liner fabric, leave a large hole for turning the bag later.
Open the corners of the outer fabric and press flat.
Mark a line perpendicular to the bottom seam about 1.5" away from the corner. Repeat for the other corner.
Sew along the line at both corners.
Repeat for the corners of the liner.
Now to prepare the closure strap... press the material in half lengthwise, wrong sides together. Turn in the raw edges to the fold and press closed. Top stitch along the edges. (For more specific directions and photos of the making of the strap, see the strap-making portion of my "Nothing-to-it Tote" tutorial.)
Pin the strap to the right side of the outer fabric, at the back seam, as seen below.
Turn the liner right-side out.
Place the liner fabric inside the outer fabric, so that right sides are together.
Line up and pin the inner and outer fabric. Sew all around the edge, reinforcing over the closure strap.
Clip around all curves and trim strap corners.
Turn right-side out through the whole in the lining, and stuff the lining into the outer fabric. Press.
Stuff the liner into the outer fabric and press.
Topstitch around the edge and tie the straps together.
Attach a big funky button, hand-sew the opening in the liner closed and you're done!!
Hopefully I'll have time to post a tutorial for the matching diaper case soon!