To calculate the weight that a building hoist can lift, you need to consider the hoist's rated capacity, which is specified by the manufacturer. This rating is based on safety factors and should not be exceeded. Check the hoist's specifications for its maximum load capacity. Ensure that the weight of the materials being lifted does not exceed this limit. Additionally, consider the hoist's mechanical condition, the strength of the cables, and the stability of the lifting points. Regular maintenance and inspection are crucial to ensure the hoist operates within its safe working load limits. Always follow the manufacturer's guidelines and safety regulations when using a building hoist.