Nowadays the application of cold form steel elements in construction is becoming very popular in roof construction, due to advantages like Fast construction, high strength to weight ratio, dimensional stability. It is vulnerable to different types of buckling, crippling, tensional failure and also leads to fire resistance. The purlin members are thin walled cross section subjected to roof loading either in upward or downward direction. The Z purlin is the most commonly used cold formed steel section for roofing system because of lapping ability, continuity, thickness of the material at support region leads to greater performance and results in economical design. The experimental investigation of the behaviour of cold formed steel roof trusses does not over a prior knowledge about either the member will fail first or the capacity of the whole truss. The aim is to investigate the overall behaviour of CFS roof truss member using finite element analysis and to predict the failure location in the truss assembly and its cause by calculating the demand to capacity ratio. Initially, industrial building is created in STAAD on basis of IS codes for selection of sections. The C and Z are the most commonly used section in the field for purlin based on the economical property. The numerical investigation of the member i.e., the non-linear analysis of element by Ansys.