5 month old lab puppy refuses to go to the bathroom outside?

Put those expanding gate things across the kitchen doors. Kitchen because there is almost always somebody there. Cover the floor with three layers of newspaper. Every day throw out the top two layers and put down two fresh layers using the old third layer for the new top layer. Feed puppy in one corner and he will eventually dump only in the opposite corner. Then you only have to paper that corner. Every time you see him dumping, tell him "Go potty" and praise him when he finishes. When this has gone on long enough, take him for a walk and take that third layer with you. Tell him "Go potty" and praise him when he is done. After that always take him for a walk at the same time and go to the same place.