Monster Maker (Unabridged‪)‬

Chancey Balogh makes all the best monsters for horror and science-fiction films and he is the man twelve-year-old Matt admires most in all the world. Because he is good with his hands, Chancey allows Matt into his studios as a kind of sorcerer's apprentice, where he works happily on some reptilian monsters called Slurks.
Gradually Matt becomes obsessed by them not their mechanics, which he knows very well, but by their very nature. Are they real?

Matt's suspicions that they are appear to be confirmed when the local hooligans invade the studios and give the monsters their chance.