So I’m not really well read at all, but for the sake of learning I’ll try to engage.

In your point about the barn becoming a restaurant, one thing to consider is the status of the building does not change without additional labour. This is what would be compensated for and at some agreed upon rate. As well, the nature of how a restaurant works is not the same as a creative work I think. If the barn was considered a piece of art and appraisals were being done, I think that would be a different story and you could imagine there would be some contention over whether the builder would be compensated additionally, perhaps through acknowledgment (which could be the causus belli for the builder and may be vehemently opposed) of their work being the at the very least involved in the cause of the thing that is being appraised.