My son asked that I make a pattern from his favorite and best-fitting shirt. It is a bit hard to see using a black shirt, but I hope you can get the gist of it and use the technique to duplicate one of your favorite wardrobe items.
Lay the shirt out flat. Run a line of pins down the center front, measuring across the front to be sure you are centered.
Using wax paper (the traditional kitchen type), line up the edge of the wax paper with the pin line you made down the center of the shirt. Pin the wax paper to anchor it to the shirt.
Using a Sharpie pen, trace the front of the shirt as shown. For the shoulder area, I found it helpful to press and feel the seam with my finger so that I knew where to place the line. Mark the front center as a fold line.
For the sleeve piece, I traced the front and back sleeve portions separately and then taped them together, as shown in the pic below.
Use your sewing measuring tape as a guide to add 5/8 inch seam allowances where necessary. (The standard width of a measuring tape is 5/8 inch.) Be sure not to add seam allowances to center front and back fold lines. Add about 1 inch to the sleeve and body bottom hem line. There is no photo, but I also traced the stand up collar piece and marked where the zipper bottom would be on the front of the shirt.
I hope this is helpful. As always, be sure to ask if you have any questions!