This diagram gives a simple and reasonably authentic pattern for a variety of garb.
Use 60" wide fabric (or sew two smaller widths together.) Consider a washable fabric in linen, cotton, or a blend. Fold the fabric in quarters, with one set of folds at the top and one fold running down the middle of what will become the front.
Take these measurements:
1. Neck to floor, or where you plan to stop (plus 2" for hem) For men, the length can be anywhere from hip to ankle, depending on the period.
2. Neck to waist
3. Neck to widest part of chest
4. 1/4 waist plus 1" ease or more (plus 1/2" for seams)
5. 1/4 chest plus 1" ease or (plus 1/2" for seams)
6. 2" for an armpit gusset
7. As wide as a comfortable shirt sleeve (plus 1/2" for seams) The dotted lines suggest neck and sleeve lines. Pick whichever seems closest to the period you are trying for. Cut out the tunic. When cutting out the neck opening, it is best to cut too small at first and enlarge the opening little by little until it is the size you want.
With the right sides together, sew up the side seams. Hem the neck, sleeves, and bottom. Put on any trim that you want. Wear it over pants and boots, or over the same tunic with narrower sleeves.