Wyrm, ask and thou shalt receive; what's more, thy cup runneth over:
http://homepage.ntlworld.com/trevor.barker/farisles/guilds/armour/mail.htm
Directions with illustrations and how-to for replicating a c. 1438 shirt of German provenance in the Wallace Collection, #A2. This is just such a shirt as Jeff J describes -- I should mention the "triangles", while one way to do it, are actually zones where expansions are placed in the weave, therefore perforce triangular. They would show up as areas where the linkrows rather gently bend as they pass through them.
For your chest measurement, figure your regular chest measurement plus ten inches -- this accommodates both aketon and doffing your shirt. You can also give your shirt some waist, and this is recommended, say, waist plus 12. You might go tighter as long as the waist isn't tighter than your chest plus your aketon when the mail at the waist is at full stretch. If it is tighter you're going to have an awful fight getting into your shirt.
By late fourteenth century, the full-on hauberk had obsolesced (many were likely cut up into smaller articles) and its compact, lightweight edition, the ha(u)burgeon, was beginning to fade also in favor of voiders, faulds, and mail standards, when our forebears came to realize just how efficient breasts-and-backs were at guarding their vitals. As the Wallace A2 shows, though, mailshirts continued to be made even though full harness of plate had stolen the show.
As a side note, those A-frame splits in hauberks in pics may be cured either by installation of right-triangle gussets, hypotenuses to centerline, on either side of the slit, or more subtly by putting an array of expansions in each half of the hauberks' skirts.