What about a garden, then a Lego house, and pics of the animals that come out at night
With a poster of what the animals eat and why they come out at night
Or a history of lighting, so he could make candle holder, oil lamp, electric lamp
Or people that work, he could make a costume
Or those people who don't work but still awake, parents with babies lol, letting pets out, toilet trips,
Hope that gives you some ideas x