Carl and the family are reading a vacation brochure in the living room during a rain storm. The roof begins leaking and water starts dripping on the brochure. This is impossible because the house is a two story. The leaking roof would drip the water on the floor of the 2nd story. Also when Eddie falls through the roof, he would not have landed on the couch, because again, it's a 2 story house.
When Carl and Eddie come up on the roof, the cut-out section where Eddie falls through is clearly visible, and remains so until he falls.
As mentioned in the above goofs, there is no way Eddie could've fallen onto the couch from the roof; however, when he did fall, he was facing the wrong way. He fell facing the back of the house and landed facing the front.
Harriette mentions that Carl ran the gas line behind the toilet when attempting to build a bathroom for Grandma Winslow but in "Mr.Badwrench" it is revealed that Carl did call a professional in the end.