Fire investigators continue to look into the cause of an overnight fire that sparked around 1 a.m. Tuesday at the Cactus Motel on Leopard and McBride.Occupied rooms were evacuated by the time crews arrived, and no one was injured. However, fire officials said the motel's layout made the blaze difficult to contain."It was a little bit of problem with construction," said Battalion Chief Kenneth Urban of the Corpus Christi Fire Department. "Multiple roofs kind of made it a little difficult."Firefighters were able to extinguish the flames in about 30 minutes.