That was on here a little while back. If I recall it was built from scrap.
Its not like he is going to sea in it,
I made a raft from two 6m lengths of 150mm drain, with a simple ply bridge and seat, oars and rowlocks. It went like the clappers. Took it up the river later, a chap passing by in a yacht said, in very plummy tones "Oh, my brother made something very like that, so you needn't think you're unique". Son was lost for words fortunately.