As I know, usually I do things the other way round XD (first design, then code, so you know what you're coding, why, and how it should all fit together)
I don't know what way around the child I'm working with is doing things but I have made suggestions and am leaving him to work out his workflow, he's coding and I'm not, currently I don't even know what the storyline is and I'm not convinced he does yet either, but if it's based on the game we're playing well we're currently still playing XD