The grande assiette is not a simple tailoring design. While its complexity is covered elsewhere on this site, here I want to share with you the lovely way that basic math can help you draft just about any complex 3-D shape from fabric pieces including the highly-pieced upper sleeve of the pourpoint of Charles de Blois. The link below opens a Microsoft Word document (.docx format) containing a 2-page worksheet showing you how to draft a customized grande assiette sleeve. I recommend you print it out for reference and for recording your measurements.
You will need to take 5 basic measurements and from those, derive 4 more. Then you will need to draw out the shapes according to the diagrams provided, using the measurements. When finished, you should have a reasonably well-fitting pattern for the upper sleeve. This is the hardest part of the whole garment, so if you can do some basic measurements, math, and drawing with straight edges and a compass (or my favorite, a pencil on a string), you can do this. Or, you can say “screw that!” and buy my pattern instead.