Underlying the rubber covering is usually a 3/16th to 1/2 inch plywood or particle board sheeting that evenly supports your weight. If your roof is metal, especially if it is the seamed type, (has crosswise seams every 48' or so), then lay a plywood strip or some wide boards (lengthwise) to walk on. This way the boards span the roof rafters and distribute your weight evenly on several supports. Be sure to check your shoes for embedded pebbles or other sharp objects that may damage the roof material.
