Summary:
Stockinette scarf knit in the round on 16" circular needles. 

Recommended Yarns:
Unger Utopia (100% acrylic): US9 / 5.5mm
Plymouth Encore Worsted (25% wool, 75% acrylic): US8 / 5.0 mm
Brown Sheep Nature Spun Worsted (100% wool): US7 / 4.5 mm
Possible color choices for each house can be found on the pattern website.

Notes:
800 yds of main color, 200 yds of contrast color.  Many knitters have cast on fewer stitches than recommended.

From the pattern website:
The Prisoner of Azkaban Hogwarts scarves are really quite different from the old Sorcerer's Stone/Chamber of Secrets scarves. Instead of even-length stripes, they have a light-on-dark trapped bar design; instead of alternating tassels, they have short, dark fringe (it's official!). The general consensus seems to be that there are 14 repetitions of the trapped bar stripe. Unknotted, Hermione’s scarf reaches her knees, so the scarf is bigger than I’d anticipated, possibly as long as 85" and about 9" wide.

Now that the fringe is confirmed, there’s no need to knit the scarf ends closed - although it does make it much easier to get the tube straight when fringing. If you’d like to take advantage of this, use a provisional (or looped) cast-on like this one when you begin, and stop a few rounds short on the first wide MC stripe. Follow the pattern, but use a three-needle bind-off when you reach the end (be sure to keep the inner sides of your scarf together, contrary to the instructions). Turn the scarf inside out and weave any ends (once you close the other end, the scarf is sealed!). Then, slip the loops from your cast-on waste yarn back onto your needle, join your MC, place a marker, and knit a few rows. Bind off this end with the same three-needle bind-off.