The commercial helicopter pilot reported that he was on a Title 14, CFR Part 91 business flight transporting one passenger and seven dogs to a remote camp. He said as he approached the camp, which was at 3,800 feet msl on a snow-covered glacier, flat light conditions made it difficult to discern topographical features on the glacier, so he elected to land at an alternate landing site at 3,200 feet msl to wait for conditions to improve. During the approach to the alternate site, just before touchdown, the pilot said the low rotor annunciator horn sounded, and he lowered the collective to regain rotor rpm. The pilot said he was unable to initiate a go-around, so he brought the helicopter to a hover, but due to the prevailing flat light he was unable to discern his height above the site, and he unintentionally allowed the helicopter's left skid to touchdown on the uneven, snow-covered terrain. He said that there was an "instantaneous dynamic rollover" as the helicopter rolled to the left, the main rotor blades struck the snow, and the helicopter came to rest inverted. The helicopter sustained substantial damage to the fuselage, tail boom and main rotor drive system. In his written statement to the NTSB, the pilot reported that there were no preaccident mechanical problems with the helicopter, and in the recommendations section of the NTSB 6120.1 form he wrote, in part: "Always keep an 'out' or rejected approach path if conditions are unfavorable on short final." He also noted that he underestimated the difficulties associated with flat light over snow-covered terrain.