I'm also around 175#s, and have walked on my roof when needed. Like mentioned all roofs are not the same. My rear ladder is rated for 300#s, but if I weighed that much, I would not use it, or be on the roof, without additional structure of some sort.
I did buy a sheet of 2" thick 4x8 polystyrene insulation. I cut it into 4 2x4' pieces. It is fairly solid, but really light weight. I set the pieces on the roof by the ladder, and distribute them where needed for service work. They are rigid, but have a little give, so feels better when kneeling to caulk etc.
Jerry