I bought my Commando on Ebay last January, completely disassembled except the engine case. Guy was nice enough to supply me with a complete factory parts and service manual, but I hadn't even owned a British twin since 1981, and had never been within touching distance of a Commando.
There are some things I would do differently on the next one, but it is doable to rebuild something without having taken it apart.
BTW - though it was a complete bike, I spent $5000 in parts. For example, rear wheel was complete. New stainless spokes, Dunlop tire, tube, bearings and chain were $300. That doesn't count the time I spent bead-blasting the hub, polishing the rim and hub cover, cleaning and re-using the original brakes, re-lacing, truing, balancing the wheel, re-packing the speedometer drive, and painting the drum and backing plate.