The other point of building upright, especially on a larger hull, is that work on both planking and interior can be ongoing at the same time, maybe not an issue if working single handed, but on a larger boat with several workers, building right-side-up can be of some benefit. For home builders, turning boats over of this size can take up a lot of time or expense. Overhead working is something that has to be done, counter-weighting tools can help. Long-boarding is an exhausting job anyway, though granted a little less painfull working below shoulder level. Pros and cons with each method.
Doing a grand job.