The shirt was one of the most basic of all
garments for the 18th century man, and, like the woman's shift, was worn as both the garment closest to the skin as well as to sleep in.  

Shirts were made of linen.  and were usually white, although a checked cloth or striped cloth was not unheard of. Like the shift the shirt was sometimes made of a very long rectangle of fabric that was folded and not seamed at the shoulder,  In other cases it was seamed and a strap was sewn over the shoulder seam, or was only made with one side seam.  As cloth was expensive and labor intensive to make, cuts were made with the economy of the fabric as the paramount concern. Many shirts came down  halfway to their wearer's knees, a way to maintain modesty as well as to keep them tucked into the breeches, as no underwear was worn  

The shirt usually had a v neck with a button to close at the throat. The collar in the RevWar period was folded over, and gathers were tucked to take the excess fabric in at the throat.  cuffs were rather narrow and gathered fabric of the sleeves.
 

Here are excellent instructions to make your own shirt by Kass McGann..  As you can see, construction is similar in many ways to the female shift and the cutting of the fabric is done economically using a long rectangle of fabric.

The Georgia Refugees show an example of a lower-to lower-middle class farmer. Here is their example of a linen shirt.

The Working Man's Basic Linen Shirt