Roofing can seem rather simple and straight forward. I mean it’s not like it's rocket science. Just show up, load your materials, and start doing the job, right? How difficult can it be? Not so fast. There are many variables that go into determining how to design and price a roof replacement. But how do you go about determining those variables. One of the most critical steps that help a roofing contractor or designer develop a roof design is the core cut.