Neither the kilowatt size nor the number of panels will reliably tell you how much material will be needed.
The best way to determine your needs is to measure the linear perimeter of the system, right on the roof. You can also use the engineering roof layout documents.
Uniform, rectangular installations require less material, in contrast to those which are irregular in shape. If there are modules that are separate from each other, this increases the perimeter, increasing the amount of material.