I think it was likely a kit that they put up themselves. I kinda thought they used it to store vehicles they were working on, until they could get them moved over to the other shop, beside CR1's trailer. The long edge of the barn could have been used to store parts out of the weather. From all indications, it seems it had a dirt floor. The long part could have even been used to dry weed. It has to be hung and dried for a period of time.
Wasn't the whole back of that barn left open? The side facing the woods.