Green Oak, and Waiting
The rule of thumb is an inch a year. For the beams of a small barn, that is a decision someone made before you were born.
Air-dried oak loses moisture at roughly an inch of thickness a year. A four-inch beam is therefore four years from the saw, and nobody has found a way to hurry it that does not show up later as a split running the length of the timber.
Kilning gets there in weeks. It also drives the moisture out unevenly, and in structural sections that unevenness is a stress the frame has to carry for its whole life.
So the stack behind the workshop is not storage. It is the part of the job that was started by whoever was here before, and the part of it you do for whoever comes next.