When we build a work barge , or pontoon barge , we tie the pontoons in with angle , and deck it with 4x4 ,s and plywood . Your angle would have to carry the span of the center load of the deck , as well as the walls and roof structure , so heavy angle . The first angle is turned in , outside flush , the 2nd turned opposite , spacing for 6' 4x4 first run , 8' spacing there after . Drill or burn a hole into the angle every so often to nail or screw the 4x4,s before decking . On your outside 4x4,s double up , after decking , frame what you want . If your house boat sets too low in the water , add some 55gl drums .
