For the reinforcement of existing factory buildings, most cases involve demolition followed by single-layer reinforcement. For double-layer reinforcement, adding purlins and purlin supports increases costs but has minimal impact on production and ensures safety. This paper uses an actual case to first perform design optimization and proposes reinforcing existing factory buildings by upgrading single-layer roof panels to double-layer roof panels using the method of purlin elevation. Then, reinforcement construction methods are applied to construction nodes, including double-layer reinforcement of skylight panels and installing flashing panels on parapets. Finally, based on practical applications, it is concluded that the advantages of double-layer roof panel reinforcement lie in safety and reliability.