The work will involve a considerable amount of disruption which the cat may find distressing. Start right away and train him to accept a cat carrier. Then you can safely transport him to a cattery to board whilst the works take place. Alternatively, set up a safe haven in a room with the least amount of disruption — such as the bathroom. Put his food, water, bed, and litter tray in the safe haven, and spritz it with pheromones to help keep him calm.