I've read many ancient texts, but I'm not sure how many of them were copied in a early Roman codex like you mention. Some Greek text from Egypt might have been originally writen in codex format already about 100 BCE. From that point in time on, the codices became more popular, quite rapidly, for new works (not only copies).
That said, many of the ancient Roman and Greek texts just start directly, many with some "provision", like this:
This is the display of the inquiry of Herodotus of Halicarnassus, so that things done by man not be forgotten in time, and that great and marvelous deeds, some displayed by the Hellenes, some by the barbarians, not lose their glory, including among others what was the cause of their waging war on each other.
I've seen this parttern quite freqüently. Also in Christian texts, such as the letter's.
Also, consider that indices and lexicons were frequently made using the first words of the referred text (see byzantine Suda Encyclopedia). Sometimes they contain complete copies of the original texts.
One codex I know, which fits as "early Roman codex" is the Chronography of the Year 354. You can browse it online. This is but a Renaissance copy of a original document, not a "copy per se" during Roman times. Yet, I think the format was preserved, since it is mentioned by the copyists. This Calendar of Philocalus is a very good example of a Codex formating in the time period you are interested in. Nevertheless, have in mind this is an exceptional document, not something anyone could understand to be of general use. Formating sure was much more simple than in this example.