According to the pilot, the helicopter was stored on a rolling dolly in a hangar. According to photographs provided by the pilot, when opened, the hangar door swings outward into the ramp area. When the pilot arrived at the hangar, he noticed another other hangar tenant had previously opened the hangar door and parked her car in the doorway. After the pilot rolled the dolly and helicopter into the ramp area, he asked the other tenant to move her car so he could close the hangar door, but she declined to do so. The pilot estimated he had adequate clearance from the end of the open hangar door and proceeded to start the helicopter and lift off the dolly. The helicopter had ascended a few feet from the dolly when the main rotor blades struck the edge of the hangar door. The helicopter immediately yawed right and impacted the surface of the ramp, resulting in substantial damage to the main rotor and tailboom. The pilot reported that there were no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation.