How To Make A Tunic: (courtesy of Legio VI)
1) Cut two rectangles of cloth. The size will vary according to the size of the legionary.
a) For a larger person with a chest of 46“, the measurements will be: 39” across by 45” long.
b) For a smaller person with a chest of 40”, the measurements will be: 37” across by 42” long. Adjust these measurements to 
your own size. (Note: reenactors invariably make their first tunics closer to a sundress than to the actual garment… most are shocked when they make a real one and find out how baggy it is! Worn properly, however, you’ll soon get over this.)
2) Sew the shoulder seams first, from the arm hole inward towards the neck. Leave the center ten-twelve inches undone; this will be the neck hole.
a) When sewing, hold the two pieces of cloth against one another, then sew a half-inch below the edge. Do this for all of your seams. When finished, pull the tunic inside out, so that all of these edges are on the inside. This is how it is worn.
b) If your material has a selvedge, use this as the top side of the tunic. This way the neck will have a naturally finished edge, and a neater appearance. This is how the Romans sewed their tunics, with the selvedge at the neck.
3) Now go to each side. Measure down twelve inches, and begin sewing down towards the bottom. Do this to each side,leaving the last inch unsewn.
4) Now fold the bottom edge over (towards you, not inward). Fold up about one inch, then sew across the bottom edge, creating a hem that will not unravel.
5) Pull tunic inside out, iron once initially if necessary. You may finish the open edges or not; I leave mine unfinished because I like the effect.
If you are confused by any of the directions, try cross-referencing this information with the directions from Legion XX's section about tunics.
Ladies:
Here's one pattern that might help:
