Roman myhtology is astoundingly meagre: most of it was borrowed from the much more copious Greek mythology. No native myth about the origin of mankind is attested. Granted, there is the tradition about the Aborigines, the ancient inhabitants of Latium, but that's hardly talking about the origin of humans. Native Roman myth remained glued to local tradition and did not develop into a cosmological system. They just mixed their local myths with the prestigious Greek ones (such as in the Aeneid).

The most common Greek origin myth presents humans as a creation of Prometheus, but note that it's not the only one. Hesiod in his Works and Days tells us of five races of Men, all created (and destroyed) by Zeus. And the Athenians were renowned for their claim to be autochthonous, literally "born from the very earth".

Even Ovid in his Metamorphoses presents the birth of mankind as a mystery:

But one more perfect and more sanctified,

a being capable of lofty thought,

intelligent to rule, was wanting still

man was created! Did the Unknown God

designing then a better world make man

of seed divine? or did Prometheus

take the new soil of earth (that still contained

some godly element of Heaven's Life)

and use it to create the race of man;

first mingling it with water of new streams;

so that his new creation, upright man,

was made in image of commanding Gods?

On earth the brute creation bends its gaze,

but man was given a lofty countenance

and was commanded to behold the skies;

and with an upright face may view the stars:—

and so it was that shapeless clay put on

the form of man till then unknown to earth.

(Ovid. Metamorphoses I, 76-88. Brookes More. Boston. Cornhill Publishing Co. 1922.)