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 3stitches on cable needle on back, knit one of left hand needle, purl, knit, purl the 3 stitches of the cable needle.

Then put one stitch on a cable needle in front, knit one, purl one, knit one of left hand needle, knit the stitch on the cable needle. Then purl 2, knit 2. Repeat this on all 4 needles.
The two knit stitches of the cable will form someting like a V which is the round part of the pumpkin.