Officials are investigating the cause of a massive fire this morning at the Walnut Creek Amish Flea Market.  The fire was reported at around 4am and it took crews from four different counties nearly three hours to put out the blaze.  Authorities say the roof of the building, located on State Route 39 in Sugarcreek, had already collapsed by the time firefighters arrived on the scene and that an estimated 50% of the 50,000 square-foot structure is considered a total loss.  No injuries have been reported.