Chris: All roofing is generally very simple. The problem with metal roofing is that where the roof joins either a wall, another roof at a different pitch or angle, a skylight, an eave or a chimney, tends to be a place where you require a lot of technical skill to be able to bend the metal such that it joins the other flashing or metal and creates a solid continuous barrier from the elements.
Homeowners that apply their own roofs are typically very proud of the way that the roof looks and for good reason. It often looks great. It’s the details along the edges and where it joins other substrates and surfaces that become problematic. The worst thing that someone can do is to install a very expensive roof improperly and have to reinstall it.
In no way, shape or form and in no case will that ever lead to a net savings because the customer will have spent the money for the roof, it will have leaked, the contractor will have to come back out and fix it and likely apply some new materials. In applying those new materials is going to incur both labor and material costs.
When you add that to your original material costs, you’re almost always going to be more expensive than having the contractor do it in the beginning. That’s not to say that homeowners don’t sometimes install their metal roofs properly. It’s just they have to be very wary of these joints.