First, an example of a shirt from the V&A. It is linen, hand-sewn with linen thread, constructed somewhere between the years 1750 and 1800.
The Regency Reproductions website provides a nice summary of Regency styles, including the details of shirt collars below.
I have a couple of patterns from books that I have been examining also, one from Costume Close-Up, by Linda Baumgarten, and another from The Cut of Men's Clothes:1600-1900, by Norah Waugh.
According to Linda Baumgarten, the shirt in her book was altered at a later date. She mentions that this is evident in part due to the length of the cuffs, so I think I will go with the narrow cuffs in Norah Waugh's pattern (minus the frills, which probably would have been detachable anyway). I haven't decided yet which pattern shapes to go with (shoulder seams or no?). I am really interested in the reenforcement at the shoulders of the Baumgarten pattern, which I could probably put in even if there is a shoulder seam. I am a little disinclined to put in that little triangular gusset at the neck without a shoulder seam...
The fabric we are using for this shirt is not perfectly authentic, it is a lightweight linen/cotton blend from Jo-Ann's, but it should do just fine. Back at the turn of the century, 100% linen would be used, but it would also have been a relatively lightweight linen, and that was just not to be found at Jo-Ann's. If I were going for complete authenticity, I would have ordered from Fabric-Store.com. They have a wide variety of linens, and specialize in fabrics for reproductions and reenactment.
I have a little bit of a dilemma to sort out before I cut into the fabric for this shirt. I want to tea-dye it (it is currently a really bright white) and I would normally just get that over with before even cutting anything, but I'm wondering if I should try dyeing it AFTER I make it up, to get a slightly aged and mottled effect... Or it could just turn out weird. Hmm.