Vest can be made for small size by using size 6 needles, medium using size 8 needles, large by using size 10 needles.
Vest takes about 14 ounces knitting worsted weight. Variegated yarn was used in the model.

Gauge
Size 6 needles - 5 sts equal 1 inch
Size 8 needles - 9 sts equal 2 inches
Size 10 needles - 4 sts equal 1 inch