Every hat i've knitted, which is about 20, I only do with straight needles.
Your basically knitting a rectangle. Whatever size you need. Then you start decreasing (k2tog or P2tog) for a few rows depending on the amount of stitches you have. When your done decreasing you take your yarn needle, thread it with the yarn your knitting with, start slipping the stitches onto it and when you get to the last stitch pull that thread through and secure the top. Your done. Below is an example of my hat pattern.
Rows 1,3,5,13,15,17: P1 WYIB SLIP 1P, P1
Even Rows 2 - 24: Purl
Rows 7,9,11,19,21,23 P2 WYIB SLIP 1P, P1 end last repeat with P2
[B]Row 25: K1 K2tog across row
Row 26: Purl
Row 27: K1 K2tog across row
Row 28: Purl
When you have the size hat you want then,
Cut yarn, thread the yarn needle through the stitches and pull it through to form the crown of the head. Secure the top with a stitch and stitch the side up.[/B]
Tip; You want to decrease on the right side rows only so it doesn't show from the front.