I like Goodwill. I like Goodwill a lot. Especially the vintage linens.
This shirt started life as a pillowcase. It's super easy, as in, you don't have to even put in sleeves easy. There's not a lot of fabric in a pillowcase, but in theory you could just slice up any piece of fabric and keep a similar height/width ratio. Here's a diagram:
I used an old shirt to make a rub off and it worked pretty well. And word to the wise, don't forget seam allowances. So once the whole thing's cut up, the only area you need to sew up is the side seams because the shoulder seam is the top of the pillowcase. Turn arm holes, collar area under, finish seams, etc., etc.
And then you're off to the races.