the thing is, you likely have a very long list of ‘requirements’ but no idea how to turn this into something good. A good builder will take these requirements, understand which compromises to make and use their skill/ experience to create something brilliant.
Or you trust your own ability and tell them exactly what you want.. but unless your a frame designer what’s the point in that? they’re almost definitely better at it than you are.
You’ll get the best outcome if you have a clear idea of what you want and then trust the builder to turn those ideas into something good.
Its the same with architecture ( my own field) let the designer do his/her own job, otherwise just hire a far eastern pipe welder. Just don’t blame them if it’s not all that you’d hoped for 🙂
btw, I’m only commenting as I have just been through a similar situation myself and my builder was brilliant.