Truss Spacing and Sheathing Type
The primary advantage to closer truss spacing is greater load-bearing ability, which is important if the roof will have heavy stuff on it, like shingles and snow. With 24" OC trusses and a conventional shingle roof, you may need to shovel your roof from time to time to prevent snow buildup from becoming dangerous. On the other hand, you can decrease this irritation by making the trusses' load lighter. One way would be to have a lighter roof material, such as metal. It will be more expensive up front, but a metal roof will last far longer than shingles and probably prevent you from having to worry about snow loads. It will also probably increase your house's resale value, which will not happen if you're simply replacing a failing roof and structure with a new one of the same or similar quality as the old one.