For those of you who fancy a go at making one of these, the proportions are as follows. The upper part of the canopy is a cone, formed from a 3/4 circle of fabric, joined and hemmed.
The band below is 1/3rd the diameter of the chute in depth, with a width equal to the circumference of the cone. The gap between the band and the upper canopy is 1/9th of the diameter, and the shroud lines are 1 1/2 the diameter. So, as an example, for an 18" chute: the upper canopy is an 18" diameter circle, with 1/4 circle removed, the band measures 6" x 42.5" ( (18 x 3.142) x 0.75) The gap between canopy and band is 2", and each shroud is 27" long. The last inch of each shroud is sewn to the perimeter of the upper canopy, then the gap, then sewn down the entire depth of the band. I tend to use 10 shrouds on chutes up to 18", and 12 shrouds on chutes above that size. The more shrouds, the better the final shape of the chute.
Hope that makes sense. Let me know if you need more info, and better still, how you actually get on with it.
Andy