Doesn't AMOS Pro come with a map editor?
I remember reading something about a map editor in a book I've got called 'Amiga Games Programming' (or something like that) it was based on AMOS or AMOS Pro. I think the map editor program it mentioned was called TOME. It stood for T? O? Map Editor. I've never seen it or used it so I'm not sure if this will write out in a binary format. Maybe worth a look though.