There is no hiding the fact that roofing is hard work. You don't have to hide from the elements. You don't have to be afraid of heights and you have to be pretty fit. However, don't get the shingles on the roof if you still have to tear off two layers of old shingles, it might be too much weight for your trusses.
Tearing off the old roof is just muscle and sweat. Applying the new roof requires a little more skill, and must be done quickly so that your roof is not vulnerable to the elements. This, along with the danger of being on a roof, makes it a difficult task for those with little roofing experience. No, it's actually not that difficult, especially with a roofing nailer and a pancake compressor.
If you're tearing off the old roof, that will be the hardest part. But definitely make sure you handle the flashing, vents, drip rail, etc. And if the roof sheathing looks or feels bad, don't try to get away with not replacing it. Depending on where you live, a composite roof should last 15 to 30 years, but it won't if the sheathing is bad.
Think of those bees or wasps that are always finding the tiniest holes in the panels of your house. Now imagine that your roof has hundreds of those tiny holes. Installing a new roof requires precision work. The truth is that anyone can replace their own roof, with the help of the many DIY websites.
Although you can install a new roof yourself, you should be aware of both the physical demands and the overall complexity of the process. Installing a new roof is hard work. Are you afraid of heights? Are you able to carry the roofing materials to the top of your house? Are you aware of the weight your trusses can support? Do you have the means to dispose of your old roof? Most, if not all, roofing material manufacturers will not warranty materials that have not been installed by a professional roofing contractor. For residential homes, roof replacement usually takes two days: the first day to remove the old roof and the second day to install the new roof.
You may have seen roofs replaced in your neighbourhood in two or three days and assume that tackling the job yourself might require another day or two, but can still be completed in less than a week, especially if you can get a few friends to pitch in. Professional roofing contractors have to install the new roof, whatever the material. If you have t-lock shingles, you will have to replace the entire roof, as they are discontinued, but your insurance usually covers the costs. The quality of the roof is also increased because you're not putting new shingles on top of the worn out ones, which means your new roof will last longer.
Here's how your contractor will rebuild your roof after stripping it down to the 3⁄8-inch plywood sheathing, or roof decking. This synthetic coating, which replaces felt paper, covers the entire roof deck and is the second line of defence against leaks after the shingles. Roofs can be replaced in a matter of days by professionals, but doing it yourself takes an indeterminate amount of time. I used a cheap roof nailer from harbor freight, and a nifty pneumatic roof cutter from Ridgid, which I found very useful especially in cold weather.
Tearing off an old roof offers the opportunity for your roofing contractor to add one of these improvements. In the case of roofs, talk to your professional to see if he will allow you to tear off the old roof at a discount. But my roof is too steep, I'd need roof jacks and planks, and it would take several days of work just an hour or two before the job each day.