I saw a television movie in the early 1970s about a teenage boy whose mother went for a routine checkup and died unexpectedly. But the boy, I believe his name was Harold, built himself a room behind the main living room wall and filled it with food and a bed, etc. and lived there. Other people came in, high schoolers have a party there, he watches everyone from a hole he has drilled through the wall. I don’t remember the name of this film, but it was scary.