All i can remember are a few specifics, would love to rediscover the title. Haven't been able to Google up anything.
- The kid (~13) made special effects models as a hobby (only one i can remember is a pair of legs which walked realistically)
- He got a sort of apprenticeship at a special effects production company
- There was a full-scale mechanical dragon model being worked on at the time, which spoke to the kid (though this might have just been one of the techs messing with him)
- Also renting space in the building was a sculptor / jeweler who befriended the protagonist
- At one point there was a break-in
- I think it ended with a fire, with the robot dragon moving on its own to save the main character
Sorry to be so vague :( There was an early-'90s UK TV adaptation, but i can remember even less of that than i can the novel.