As with other military items, consult "Echos of Glory" (Union edition- pgs. 126& 169, Confederate edition- pgs. 93& 154), "Uniforms of the American Civil War" by Field & Smith (pgs. 171, 174, 177, 183, 201, 212, 225, 226, 227, 228, 233, 245 & 251)
Most of these shirts are depicted with pockets, either patch pockets or welt pockets. A photographic example can be found for most states of the Confederacy. You should check (or have him check and carefully notate) the exact needs of his particular unit, troop, or battery.
In civilian examples, the reproduced example from the Steamboat Arabia has welt pockets, on a slant. Several photographs of men in over-shirts include pockets, though I'd need to look around for the exact shirts I'm referencing. ("Firemen" shirts and some popular with the Miners 49-ers come to immediate mind)
For a decent "Shirt on the Square" pattern, try the "Work Woman's Guide to Plain Sewing" (it's available on Google Books and frequently referenced here), "Thoughts on Men's Shirts in America" (which is a fabulous basic book on shirts of all sorts), or the Martha McCain Fashion Historian pattern (out of print, but often found on ebay and pattern re-sale websites).
...and let's wrap up the discussion of a military item before we get a polite reminder about the focus of this forum.