Well I used a sideshow armored body for my so it might be slightly different depending on which body you are using.
Materials
-sandtrooper/stormtrooper feet
-white nylon fabric
-diaper cotton or fleece
-sewing machine
-boots with soles that can be removed
-strips or styrene
-white paint
-white elastic
-fine warn
I got a pair of sandtrooper feet and sculpted the rough shape of what the boots toe would look like. It doesn't have to be detailed as it will be covered in fabric anyways. Here is mine at that stage...
Make sure that you fill in the space between the heel and sole is filled in. This is the base of the boot.
Next you need to make the fabric parts. My boots are actually 2 parts, the top and the bottom and are joined behind the bottom strap. For the bottom that raps around the foot, cut a rectangle piece of nylon that will wrap around the feet you made earlier. Then cut out a notch in the back so the fabric will fit around the peg and meet in the back. once you cut that hole you will need to sew on the strip that runs to the toe. on the front side of the piece, cut it into a semi circle and cut lines into it every half inch or so. This is for when you are gluing the fabric to the shoe.
When you are happy with the look of the bottom its time to glue it down. I just used super glue but in very little amounts. Start by gluing the 2 back flaps that wrap around the peg to the back of the heel. Make sure you fold over one end of the flap so that it doesn't have a rough edge. After thats done, start gluing down the outside edges. start with the toe and work your way around. Make sure you pull the fabric tight so there aren't any wrinkles.
Once you get both feet done like this take a pair of boots like you like the sole of and remove it from those boots and glue it to the bottom of your boots. You might want to paint them white first. Then wrap a strip of styrene around the boot where the sole meets the fabric.
I'll do the second part a little later. Its a bit easier.