Roofing products are made for specific roofs and the talent a roofer is following the specs of a particular product well. Some roofers are natural at getting a idea of how things work. All make a mistake at one time but I find that if learned well it’s never done again.
Low Slope or flat roof contractors should have a good knowledge in one of the products that are to offer for flat or low slope roofing. Tar and gravel, torch on and metal are the predominant products out there. There are some other products on the market but definitely not the majority. I have even heard of folks out there converting there flat roof or low slope into a garden, I don’t how? but they did. This is a dangerous job regardless of the product, each holds a different danger. Tar and gravel requires some pretty tar being pumped up to your roof, if the roofer is no paying attention well, some pretty nasty stories have occurred even on my experience. Torch on is attached through high heat, meaning a flame. It is well documented that a torch on roofer can singe insulation in a building and leave for the day. Two or three hours can pass before the slow burning ambers in the insulation can reignite and burn the building down. Metal is strong and lasts a lifetime, high winds during installation has caused injury
Somewhere in the mid slope and high slope is the largest array of products available to the consumer. I can only speak for the Metro Vancouver region and will explain their array of products. The most common is probably debateable but I will start with the product I feel is the most used and that is Asphalt. Asphalt is a fibreglass or paper based product that is soaked in asphalt and then granulated. This is the most common used product in my option due to the strong warranties and affordable products. Remember that no slope roofing product can be placed on a flat or low slope roof. This is typically a safe product for your home and the roofer if he is roped up and paying attention on the job. The one warning is asphalt left lying on a deck on hot sunny days can be disastrous.
Cedar shake is the second most used roofing product in the greater Vancouver region with new construction taking the largest responsibility. Cedar too is a safe product to install as well as long as the roofer is wearing protective gear, not necessarily because they might get a splinter but because if the cedar has been treated I have seen roofers turn a funny colour after touching too much fresh cyanide all day. It is safe for you they spray it on children’s playground equipment too. it will eventually be safe to touch, just not right after the process.
Slate is not so common of a choice for re-roofing unless you stuck with one. New construction has had a thing for slate so you do see it around. It is not very common in the Greater Vancouver region because we have cedar shakes and they are easier to process, install and replace. In all situations the danger of a slate roof is that a piece falls and lands on someone. On a regular day very unlikely.
Metal can be installed on a steep roof, there is rubber roofing with some companies selling a rubber moulded shingle which is quite impressive. I am sure a roofer must be well trained in installing this product and like asphalt this shingle seems quite safe as long as the roofer is paying attention.