The pilot who held a commercial pilot certificate with single-engine land airplane ratings was receiving training to obtain a helicopter rating. The pilot had 31 hours of helicopter flight time and the accident occurred on his second solo flight. The pilot reported he was attempting to takeoff from a wet grass area when the accident occurred. He stated that when he increased the collective to lift off, the helicopter began to roll to the right with the right skid still on the ground. He moved the cyclic to the left and the helicopter responded by rolling to the left with the left skid contacting the ground. The pilot then applied right cyclic and the helicopter again rolled to the right. The right skid contacted the ground and the helicopter rolled over onto it's right side. As a result of the accident, the main rotor blades and the helicopter fuselage were substantially damaged. The pilot reported that there were no preimpact mechanical failures/malfunctions that would have precluded normal operation.