Common rafter layouts use the Pythagorean Theorem to determine the length of the rafters needed for building a roof at a given pitch. Calculate rafter lengths and design a workable rafter layout for a certain roof pitch with instructions from an experienced builder in this free video on carpentry. Expert: Robert Markey Bio: Robert Markey earned his BS in Physics from MIT in 1969 and his MS in Computer Science from the University of Massachusetts in 1982. Filmmaker: equilibriofilms Erik