Fortunately, I answered this in another thread about a month ago.
Heres the pattern (Men's size 10) at 50% scale.
You will probably need to adjust the pattern to fit your shoe size, but it shouldn't be too difficult. I would try it as a paper pattern first, then make alterations based on the way that fits.
1. sew the base and the ankle together. (the ankle strip will be longer than the base due to poor measuring on my part. Just trim off the excess and it should work fine. )
2. sew the back of the connected pieces together, making a sock-like shape.
3. cut out a rectangular strip of craft foam measuring 1.5"x7.5"
4. fold the toe cuff in half over the strip of craft foam and sew it inside.
5. sew the toe cuff to the toe edge of the base.
6. roll the ankle cuff so when it is flattened it measures 1.5 inches wide. (make sure you have at least a quarter inch leftover to sew to the base)
7. sew the ankle cuff to the base.
8. fold the bottom edge of the base in about a quarter inch, then sew along the bottom edge of the base to finish it.
9. hot glue the bottom of the base the sandal (make sure you've adjusted them to fit before gluing).
10. enjoy your sandals.