Let's begin with fabric. In the Original Series, the actual fabric was a stretch velour type of fabric. My first uniform I made was of this fabric. Looks good, but wears bad. The first time I washed it, it shrunk. I found that a polyester/cotton blend works just fine, but make sure it is of good quality.
Always buy white so you can dye the fabric as close to the colors as possible. This takes some doing, so buy inexpensive material so you don't ruin the good fabric. Remember in the original series, the colors were not what we thought we saw. Example,Kirk's tunic was a mustard/green color, but because of the film, it looks gold. So for your purpose, you would want to dye it gold, we never actually saw the mustard/green.
You should always pre wash your fabric, dye it, then lay your pattern out. Most patterns can be purchased at conventions, but I prefer to get mine through LINCOLN ENTERPRISES. Make sure you know your size. No cheating, these tunics are not forgiving, if your a large and you think your a medium,it will be extremely tight and not look good. Read the instructions carefully and begin sewing.
This tunic is a very simple piece of clothing to make. To get the black band around the collar right, you may need to snip the ends at an angle going inward. This will make the collar hug your neck, and it should hug your neck and not be loose. If you really want the authentic look, you'll want to sew in the invisible zipper. If you have sewing experience, then go for it, otherwise, buy your fabric in a stretch. This way you can pull it over your head. Now all you need to do is attach the insignia and rank braid and you're finished.