Having sewn various items for a booth at our Renaissance Faire, I can tell you my biggest problem has been trying to decide what sizes to make. Usually, the smaller sizes don't do as well as the XL. Go figure. If your friend can give you a ballpark figure as to how many of each size you might need, that would help out.
That being said, the closer you can get to "one size fits most", the easier for you.
The Wikihow link that osewme posted is a pretty basic pattern for a tunic, but once again you are relying on a T-shirt size to get you started. Also the neckline on a T has stretch and depending on the material you are using, you may find the neckline is not big enough for most guys heads. Making a slit in the back about 4 to 5 inches helps, but cutting larger is better. Of course, finishing off the opening is more time involved on your part. Short sleeves or long sleeves, seamstress choice, depends on the width of fabric you have to work with.
Tabards are some what easier as there are no sleeves and no side seams. They are worn over other clothing and are fastened loosely with a separate belt, not part of the tabard. They can be cut with the fold at the shoulder eliminating a seam, or cut in 2 pieces and stitched at the shoulder. Again, seamstress choice because of fabric size. I did a search "how to make a tabard pattern" and got lots of hits. The PDF from amtgard is a good one, but it's pretty wordy because they are assuming you don't know how to sew.
When cutting, don't worry about being too accurate. Stack as many as you can safely cut, use a new blade in your rotary cutter and go for it.
As far as I'm concerned, all of the above is the hardest part!
If you have a serger, use it. Saves lots of time. I serge the edges and then just fold that over and straight stitch it down. You can finger press to save time. Both sides, hem and neckline, too if it is cut large enough. No facing for the neckline then. Remember this is a costume, you are not really sewing for the king.
Hope this helps you somewhat. Wish I was in the neighborhood, I'd be glad to help you out!