The ribbing that is found on sweaters can be done in crochet. For this example I used a smaller hook for the ribbing than I did for the sweater body.
To Begin: Ch 13.
For Row 1: Sc in second ch from hook and in each ch across. Ch 1, Turn. (12sc)
Row 2: Sc in back loop only of first st and each st across to last st, sc in both loops of last st. Ch 1, Turn.
Rep Row 2 until you reach the length you need. In ribbing, the length equals the width. That is because you turn the ribbing around and changing hook to a larger size you then work the sweater up from there.