This study was carried out to determine the key challenges which contractors face in the planning, purchasing and acquisition of building materials, a case of General Building Contractors within Nairobi County. Data was collected using a questionnaire that was administered through ‘drop and pick’ method. Percentages and frequencies were used to analyze the data collected. The findings were presented in tables and graphs. Descriptive statistics and inferential analysis were also used. Some of the key findings of this study were; procurement risk, project complexity, stage of construction, project objectives and project constraints were found to be amongst the vital factors considered during procurement planning. It was found that material procurement strategy was being influenced by accountability enhancement, cost of implementation, information accessibility and ease of application and that contractors pay keen attention to the suppliers’ price, quality, reliability, strategic relationships, efficiency, flexibility and risk management; all which are equally necessary to be considered during procurement of construction materials. The firms were found to be involved in strategic planning which would consider and forecast procurement risk that would be experienced so as to give room for development of measures for mitigation and contingency planning; planning also cut across the consideration of project complexity to give room for the formulation and strategizing of a suitable managerial approach, the stage of construction, project objectives and project constraints. Some of the major conclusions were that when procurement best practices are put in place, it would reduce or rather curb these challenges. Procurement best practices incorporates procurement risk management, planning and supply performance influence organizations that aims in achieving the collaboration and communication capabilities while sustaining the responsiveness capabilities of market-oriented governance structures. The researcher provided recommendations such as the government should advise the financial institutions reduce interest rates, they charge on loans to an affordable level so as to enable contractors secure loans that could be used in sufficing project funds thus dealing with financial constraints