Step 1: Supplies
You'll also need a length of 1 inch nylon webbing for a belt, (like that used on backpacks) long enough to go around your waist, plus about 12 inches. You will also need a plastic buckle for the belt.
To make the pattern you will need a very large sheet of paper. I used brown kraft paper (the kind used to wrap boxes for shipping, usually found with shipping supplies). You can also use wrapping paper or tape together some sheets of news paper.
Finally for construction you'll need the usual stuff for sewing, Sewing machine, thread, scissors, etc...
Step 2: Making the Pattern & Cutting the Pieces
If you want to make these large enough to go over another pair of pants then make 1 long cut from the bottom of the leg to the waist and insert a 3 or 4 inch spacer.
I'm sure your wondering how much fabric you will need. You will be cutting 4 of these pieces from each of the 2 fabrics you choose. If the widest part of the pattern piece is less than 15 inches you can use a 60 inch wide piece of fabric that is slightly longer that the total length of the pattern piece (get the fabric at least 2 inches longer than the pattern piece) If the pattern piece is wider than 15 inches, or you chosen fabric is less than 60 inches wide, then you will need the get the fabric cut to slightly larger than twice the length of your pattern piece.
For the liner I used a 60 inch wide piece of fabric and you can see below how I was able to get my 4 pieces cut from it.
Step 3: Sewing the Pieces Together
You will make 2 stacks of fabric, stacked in a specific order and they should look like mirrored images of each other. Start by placing a piece of liner down (good side down if it has a good side) with the crotch pointing to the right. Then piece of the shell down (good side up if it has a good siide). Then place another piece of the shell on that (good side down) and finally another piece of the liner down, (good side up). You now need to make a second stack exactly the same way, but with the crotch pointing to the legt. (liner (good side down): shell (good side up): shell (good side down): Liner (good side up).
Now I found it easier to sew together the shell and a flier and work it a 1 piece instead of 2. Once all 8 pieces are sewn into 4, you can start making the pants. Begin by taking your first 2 pieces and sewing them together. Sew the inside of the pant leg from the crotch down to the bottom of the leg. Then sew the other leg in the same manner.
Next, fold the legs out and place the 2 pieces together with the shells facing each other. Sew together the crotch. The best way to do this is to line up the seams in the center and start there. Sew from the center seam to the outside of 1 side, then return the the center and sew to the other side.
Now you'll have to sew the outside of the legs. Before you do that though you'll need to kind of turn the pants inside out. If you fold the piece so the linings are together you should havfe something resembling pants, then turn them inside out. See the pics below to how your piece should look.
Then simply sew down the outside of the leg.
Step 4: Making the Waistband
Next fold the waits band down 2 inches to the inside if the pants and sew all the way around. This will create the opening for the waist band to go through.
Once the waist band is created you will need to pull the web belt through the waist band. You can use a wire hanger or even an extension cord as I have used here. Anything small , long and flexible to make it through the openings.
Pull the belt through and attach the buckle. Now just hem the legs and you are done.