Add support bracing for roof

Hi, I am going to be working in attic with insulation and while up there I am thinking of adding some extra support for my roof. It is all open in the attic right now. The size is roughly 27' long gable to gable, and 26' across. It is a standard roof with 2x6 rafters and the joists run the same direction as the rafters, although they do not all meet up evenly as the spacing on everything varies. I do have a wall in the middle of the house that has support all the way down to the basement floor. I was thinking of maybe only adding the extra support in the middle 1/3 area of the roof since the middle would be the weakest part where a heavy snow would start to collapse? Is there a usual way to go about doing this?