Not strictly a 'how to draft a T-shirt from scratch' but a great introduction in how to modify one pattern to another. It's always good to have a starting point you know well. And I love the bodice of the Moneta.
Second video illustrates fit revisions, and how to draft a few versions: Dropped Sleeves, Neckband, V Neck, Scoop Neck fitted.
Third Video is Sewing them. Visit the Project Info for more on these here.