A resourceful guy built some furniture completely out of FEDEX boxes.
Then he built a website named FEDEXFURNITURE.COM.
The analysis likely differs for furniture made of boxes he receives directly from FedEx and boxes he comes by after they’ve been used. Exhaustion doctrines would apply to ‘found’ boxes. Also, when you order supplies from FedEx, you enter an agreement to use the supplies for shipping, not furnishing your home (note that FedEx alleges breach of its TOS and this may rise to conversion as well (no pun intended)).