For purposes of 1. Playing at a GW store and 2. Playing at a tournament, how much of model must be from GW products? I've got an Ork army, an abundance of kids toys that look cool, and the desire to make vehicles, but I just wanted to see if there was some kind of rules against using non-GW bits. Everything I've made so far is 30-50% non-GW parts.

Thanks!