Dr. Perumalla, you could consider using the flowing parametrs: the uniaxial compressive strength, tensile strength, and the thickness of the roof; the length and width of the extracted space of the longwall panel; the mining speed (i.e., the advance distance per day). 

D. Xuan

You need to ascertain the cavability of roof rocks by combining geo-mechanical data with ground water conditions and extent of immediate roof.. Geo-mechanical data must stress on the nature of roof, type and thickness of roof layers, presence of joints and geological anomalies along with the rock strength parameters.

Another set of data would be operational data, namely, the length and span, type of machinery deployed, rate of roof exposure etc.