To get it in the cone shape, I just cut along a radius, folded it to the right curvature, and thencut out some extra material on a radius (think of it as cutting a slice out of a pie).

For those guys berating my use of a disc in the front, firstly, I'm a pretty big guy and I can handle the crosswinds- and also, you realize that a disc in the front saves a LOT more energy than a disc in the back, because the wind is still "pristine", right?