Weaving is a good way to make a nice looking top hat. It isn't overly difficult but it takes some practice to get the results you want because it is critical that your bubbles are near identical in size for a clean look. Check out
www.balloonhq.com and
www.mbd2.com also there are DVDs out there on balloon weaving although I can't remember any of their names right now. I think Rebecca Kanar might be in the Chicago area and I know she is a very talented balloon artist.
Basically you start with 6 balloons tied together at the knots. These form the ribs of the hat. choose one and make a small ear twist where the knots are and then choose another balloon and make another ear-twist on the other side of the knots. This hides the knots as well as keeps the structure flat. Take a new balloon wrap it around one of the spines about an inch or two away from the knot mess (that is the center top of the hat.) make a small bubble as as spacer and then wrap it around the next spine, repeat, repeat and repeat again and again and again. Work in a spiral outward. When you think the top of the hat is large enough around put an ear twist in all the spines so that they all bend 90 degrees ( in the same direction) and contine to spiral around the hat adding balloons as needed. When you are ready for the brim make another ear-twist in the spines. Good luck.