The pilot landed to the south on the turf/grass area alongside runway 18. During the landing rollout, the airplane encountered a wind gust and cartwheeled. The pilot stated that the airplane was traveling at a "fairly slow speed" when it encountered the wind gust. The tricycle-landing gear airplane came to rest upright and the pilot exited without injury. The cabin roof was crushed, both wing spars were bent, and the engine firewall was damaged. The local area winds were out of the west at 8 knots, gusting to 16 knots.