Purchase a pair of red or bright green tights. If you cannot get coloured tights, then you can always dye white tights red or green with some good quality fabric dye. Buy an over-sized red or green pullover or t-shirt. In addition to this, get a regular sized long sleeve green, red or striped turtleneck. Remember that the turtleneck should be green if the over-sized shirt is red and vice versa. Buy the shirts from any departmental or thrift store. Collect ribbon and bric a brac to give some contrast to the shirts. It can be gold or a mix of green, red and gold.
Trim the over-sized shirt
Convert the over-sized shirt into a vest by cutting the sleeves in a zigzag pattern. Trim the cut edges of the shirt after that. Add the ribbon or bric a brac to the front and near the sleeves with some fabric glue or by using a sewing machine. Make a Christmas design or mark the edge of the costume. Attach a piece of ribbon around the waist for the belt. Purchase or make an elf hat as well. Cut a piece of felt into equilateral triangles. Cut 6 pieces of felt 4 inches wide and 8 inches tall. Attach these to make a cone. Sew a pom pom or bell at the top of the hat.
Make a pattern to remove the fabric for the shoe. Choose felt as the fabric if you want it for inside use. However, if you are going to wear them outdoors, make the shoe without a sole in order to fit over a shoe. Make sure you leave space for the seam and install a bell at the tip of the toe.