Re: Can you use siding on a roof with a normal pitch, instead of roofing materials?
There's a reason for differences between roofing and siding materials.
In part the materials themselves but also the way in which they are fastened.
Siding materials are designed in both materials and fastening to peform in a vertical orientation. They will shed water better on a vertical wall than say a horizontal plane like the roof.
For example you mentioned vinyl -- vinyl will distort with exposure to sun and temperature --- also the method of fastening each course doesn't provide a tight seal against water --- not a big deal ( so to speak ) when on a vertical wall.
However , place the same material on the roof and you will have major water leaks. Never mind it wouldn't stand up to foot traffic while being laid or any subsequent maintenance on the roof. Besides , when the vinyl distorts the roof would look crappy with all the waveness.
Your better off sticking with using products intended for roofing. They are designed to overlap properly forming the proper water tightness preventing leaks along with the materials are selected to withstand the harsh exposure being on the roof. Leave siding material for the walls.
2 cents worth.
"" an ounce of perception -- a pound of obscure "