[mmikeff]

Depending on how complex his vision is, you might be able to do a chunk of this in side someone else's game, Roblox, MineCraft etc. I recall my daughter spending loads of time in Roblox games that other kids had made, so long as the game logic is not to crazy you might just need to arrange objects and let the existing 3d controls take care of the hard part.

Also, top commenter is right, the game won't get finished so aim for an achievable goal that is interesting in it's own right.