Pattern for only one size but easily adaptable for other sizes.

The chart might be a bit confusing: the cable-row is to read:

knit 2, purl 2, put 3 stitches on cable needle in back, knit one of the left hand needle, then purl, knit, purl the 3 stitches of the cable needle.

Next put one stitch on a cable needle in front, knit one, purl one, knit one of the left hand needle, knit the stitch on the cable needle. Then purl 2, knit 2. Repeat this on all 4 needles.

The two single knit stitches of the cable will form someting like a V which makes the round part of the pumpkin.

The rows are numbered on the left, but as you are knitting in the round, the chart is always to read from right to left.