Many many years ago I worked part time for a carpenter after my day job. One beautiful summer evening he and I and a couple of other guys tore the shingles and felt off of a roof on a house preparing to change the pitch and do a re-roof. We were almost finished and had about an hour of daylight left when a storm front moved in. Wanting to keep the interior of the home dry, we went to the local hardware store and bought tarps to cover the entire roof deck. What was available were huge blue plastic tarps, about 40 X 40 which worked quite well.
but as we were buttoning up the ridge, the rain started.
What we had done was created the worlds largest slip and slide. One step on the wet tarp and off the roof you go. All of us wound up on the ground at one point, sliding off the end into hedges or flower beds. Fortunately nobody was seriously hurt, some scrapes and bruises.
But the sight at dusk of people standing on the roof....then just disappearing is both unforgettable and funny.
We paid more attention to the weather forecast after that.
And as far as metal roofs.....when ever we had to work on them we rubbed a bit of gasoline on the soles of the work boots. It softened them up just a bit and made them "stick" to the roof. (never on painted roofs, just the galvanized tin types.)