Assume he's a Syrian hamster? Our last Syrian grew huge and got stuck in tubes! Tubes made for hamsters usually are too small for syrians - they do much better with rat sized tubes and toys. Tube diameter is best about 7cm diameter. Minimum 6cm diameter. House entrances or other toys with holes, the holes need to be at least 6cm diameter. They don't need to be fancy tubes and tunnels
Pringles tubes are good (cleaned out). Or a kitchen roll cardboard inner tube if you slit it down the side longways so it expands. External tubes on cages aren't good - they tend to block them up and pee in them and are an escape route, and it stops them having normal behaviours (eg nesting and hoarding on the substrate).