Ah, well it's called "Neolithic Cut" and it kind of works like this.
There's an argument that in Northern Europe garments were first tailored from skins, and since the mindset/ pattern skills that use skins for clothing are markedly different from the ones where clothing is constructed from narrow woven panels of the original backstrap looms, the cut is very different.
The Neolithic Cut is basically a one piece shirt pattern that has no shoulder seams to leak, or to rub under pack straps, and it is incredibly economical of fabric too
You can get an idea of how the pattern fits together if you make this first;
Take a square of paper, say A4, trimmed to size.
Now fold over a piece about a quarter of the sheet right across.
Using that folded over edge as a guide tear the paper inwards a quarter of it's width from either side, and fold these pieces in.
You've made a T shape.
Cut out a small circle at the centre top of your first fold witha short straight cut down the front, that's the neckline.
Narrow the sleeves from the cuff to the underarm tearing off long triangles. These triangles become the collar and cuffs, the neck piece becomes the gores for the side hems, and if you leave a bit of the chest seam open you can sew in a pocket with a covering flap at your chest.
The only seams are from wrist to wrist and straight down the front. The rest is just comfort fit as one chooses.
Use fabric instead, result, one Neolithic Bushcraft shirt from a metre and a half of 150cms wide cloth
The two crucial measurements are that the cloth wide enough to go around your chest/ tummy, and make sure the first fold over is deep enough to fit around your underarm without either girding free movement or being too loose. Try to keep the neckline small, the front slit allows it to slip over your head so it doesn't need to be as big as that. Make the neckline a bit deeper at the front than at the back.
If the fabric is too wide, strips can be cut off the front to narrow the body, and if you want a full length front opening shirt just finish the front edges with buttons/holes or a zip or lacings.
cheers,
Toddy