A lot of costumes, such as pirate costumes, really need boots to give the outfit a finished look. However, many costumes don't come with foot gear, and boots can be expensive for just a single use. A relatively easy and inexpensive alternative is to fashion boot covers that are worn over regular shoes -- usually a type of dress shoe as the toe and sole may show. Boot covers will look best if you can find some fake leather in a colour to match the intended shoe.
Measure around the top of your calf (or as high up as the boot cover will go) and measure around the ankle. Add to this 6.2 cm (2 1/2 inches) for a seam allowance and for some slack, as the boot cover should fit loosely and not tight. Cut out the leg portions of the boot covers by making a trapezoid in which the top (widest) portion is the calf measurement -- plus the 6.2 cm (2 1/2 inches) -- and the bottom is the ankle measurement -- plus the 6.2 cm (2 1/2 inches).
Take your shoe and make a pattern for the foot covering portion of the boot covers. Lay the shoe on its side and cut out two side shapes per boot cover. Remember the side has to be long enough to curve around the heel to the back seam. And the top of the side cover has to be able to go over the top of the foot, halfway. Once you make the pattern, add a 3.7 cm (1 1/2 inch) seam allowance all the way around. Cut out the shoe portion sides. You'll have 4 sides total.
Sew a pair of the shoe sides together along the top seams. Now you have a piece that should lay across the top of your foot and down the sides, and at the back (heel) the pieces can be wrapped back to meet ends. Sew all pieces with a 1.5 cm (5/8 inch) seam. Sew the other pair together.
Sew one of the foot covering portions to the bottom (ankle) of the leg covering portion. Now you have a covering that covers your leg and foot if wrapped back. There should be ample overlap at the back.
Sew the other one.
Sew the back seam on the boot coverings. With the added space, the boot covering should be loose enough to slip over your foot and leg. Note: You'll put the boot covering on before you put on your shoes.
Turn under the top edge of the boot covers and stitch it down to have a finished top, instead of a raw edge. Do the same for the bottom edge. Finish both boot covers.
Add elastic at the instep to help hold down the sides of the boot covers. The elastic is worn under the shoe. So put on the boot covers, flipping the elastic up and over the foot while you put on your shoes, then stretch the elastic under your shoe to hold the boot cover in place.