01
Measure the lines as well as the planes
A simple gable roof and a roof with many intersecting wings may contain similar slate areas but different lengths of junctions. Ask for ridge and hip lengths to be measured along the relevant lines, not inferred from the square count. Specify which ridge treatment is intended before translating those lengths into material quantities.
02
Keep each detail on its own schedule
A schedule can list field slate, hips, ridges, valleys, and penetrations separately. That makes a change in roof shape easier to price without replacing the entire estimate. Where a piece-based ridge system is selected, its actual exposed coverage determines the count. A generic field-slate quantity cannot establish how many ridge components will be needed.