Something like that I think you would have to use a temporary tie off points on the roof. Something like the Miller RA-15 anchor. It seems extreme for a gutter cleanout, but falling off a roof is no joke. That slope wont even allow a rough terrain scissor lift, if it was off a lift it would need to be a snorkel lift with enough range to park at the high point and reach horizontally along the length of the house. Is there gutter to the sides of the deck facing to the trees (right side of the photo)? The temp anchors are good, but you also need the homeowners permission to install as it is basically punching holes in the roof to be repaired when you remove it. Also you should have fall protection training to install and use the harnesses to move around when your up there.