Step 1 was to draw over my shirt through brown paper and cut it out.
Then it was trial and error really. Not too many errors thankfully. The back of the top is a knit fabric, so I used my walking foot and zigzagged seams together first before straight stitching them. About four hours later ... voila! Almost like a bought one.
All in all, not bad for an afternoon's work and about 2 metres of fabric.