Three words..
Pitch, pitch, pitch!! The covers I've seen from the top Shop are generally a fairly sloppy fit when compared to Fairclough and fit is important in a winter cover.
Perhaps in the mid west the snows are not wet and heavy but here in Maine I've seen 6" collapse covers due to the saturation and moisture in the snow. Winter covers from Fairclough are expensive but also a good value. A cover for my boat is $2400.00 +/- and will last more than ten yeas if well cared for and a shrink wrap cover is $700.00 each winter. I still choose to shrink wrap because I do not want even canvas in contact with my Awlgrip painted hull all winter..
My only gripe with the custom canvas covers is that they never have enough pitch and will usually require internal snow braces in addition to the regular frame. Also the canvas does not shed snow like a shrink wrap cover does.
If you decide to make your own cover just remember:
#1 Pitch
#2 Cross ties at stanchions (prevents snow load from breaking or bending stanchions inward)
#3 Breathability and ventilation
#4 Perimeter board - prevents cover from resting on stanchions and poking through or loading/stressing the lifelines.
Cross ties:
P.S. I know I spelled perimeter wrong but I suck at MS Paint and spelling was the furthest thing from my mind.
Good Pitch:
The material and the design are the two biggest contributors to snow shedding. Shrink wrap sheds snow like crazy.
This particular custom made Fariclough cover has a lower than ideal pitch, I've seen some made by the same folks with a much higher pitch, and when we get freezing rain that then turns to snow things like to stick to the canvas. Nothing beats cotton duck though for breathability!!
Minimal/Marginal Pitch:
If you build your own don't cut corners. These are all home made failures!!
Top Shop vs. Fairclough on fit..
Top Shop Cover: (photo courtesy Top Shop)
Fariclough Colver: (Photo Courtesy Bob S.)