Tool for marking large flat building material sheets

A tool for use in marking large flat building material sheets each sheet having atop and a bottom surface, standardized length “L” and a standardized width “W” and having opposed longitudinal side edges, the tool serving to provide a cut line by which each sheet can be dimensionally shaped for installation on a building roof or gable, comprising:

• an elongated unitary bar providing at least one straight uninterrupted edge and having a top surface and a bottom surface, the bottom surface being configured to be positioned in contact with and slide on a building material sheet top surface;
• a first pin affixed to said bar and extending perpendicular thereto;
• a second pin affixed to said bar and extending perpendicular thereto, the spacing between said first and pins being adjustably variable, the first and second pins each having an enlarged head portion extending from said bar bottom surface and being configured to slidably engage opposed longitudinal side edges of a building material sheet so that said bar straight edge extends at an angle to said building material sheet longitudinal side edges, said straight edge providing an edge for marking a said building material sheet to provide a guideline for an angle cut, the angle being selectively determined by said spacing between said first and second pins.