I created a Volunteer Span-AM uniform some years ago.  Long enough ago that I was able to buy some of the surplus uniform parts used by cast members in John Milius' movie "The Rough Riders".  In studying the issue, I came to the conclusion , based on photos of actual participants, that the Volunteers, especially the officers, had a pretty wide latitude in what they wore.  I've seen pix of a dozen Volunteer officers with no two uniforms quite alike.  Some differed a great deal.

Allow me to give you some advice in recreating your uniform:  I STRONGLY suggest you base your uniform on photographs of actual participants.  DO NOT rely on anything else, be it movies or paintings, or color plates reproduced in books.  The reason for this is that at some point, some self-appointed "expert" is likely to will approach you and offer the kind advice that some aspect of your uniform is not "period-correct".  To the extent that you base your uniform on contemporary photos, you insulate yourself from these pesky "thread-counters" as they are called.  Keep a laminated copy of the pic or pix upon which you based your uniform in your pocket, show it to the thread-counters, and you shouldn't have to say a word to them.

Go to amazon and google "uniforms of the spanish american war", and a few books show up.  I believe I used the one published by Osprey, but the others, assuming they have lots of pictures, will be OK.  The color plates are OK for, well, colors, but the actual uniforms should be passed on pix of actual participants.

Good luck to you!

That's true.  Still, the Regular officers had generally well-known and well-understood standards by which to have their uniforms made by the clothiers who supplied the uniforms for the Regular officers.  Enlisted men had much less latitude in their issued clothing, of course.

The Volunteer Officers, on the other hand, had uniforms that were deliberately different from regular uniforms, and the descriptions of the Volunteer Officer uniforms were inexact enough so that a wide variation can be seen even with the same "standards" being used for Volunteer officer uniforms.  The pictures tell the tale.  What happened was that the various officer uniform outfitters took the description of the proper uniform for Volunteer officers, and interpreted it as they thought best.  The same outfitter, making a regular officer's uniform, had a much better set of guidelines to go by when making the uniform.

There was much less variation in the uniforms of the Volunteer enlisted, because their uniforms were either Regular Army hand-me-downs, which were uniformly alike, and/or because the Volunteer enlisted uniforms were more simply constructed so less variation was possible.

Interestingly, some Volunteer Officers never got a full officer's uniform until they were waiting to be mustered-out after they got back from Cuba.  A LOT of the uniformed, group pix seen in the books were not taken in the field, but back in the US.