From Wikipedia:
"The
Romans developed the form from wooden
writing tablets. The gradual replacement of the scroll by the codex has been called the most important advance in book making before the invention of
printing.
[2] The codex transformed the shape of the book itself, and offered a form that lasted until present day (and continues to be used alongside
e-paper).
[3] The spread of the codex is often associated with the rise of
Christianity, which adopted the format for use with the
Bible early on.
[4] First described by the
1st-century AD Roman poet
Martial, who praised its convenient use, the codex achieved numerical parity with the scroll around AD 300,
[5] and had completely replaced it throughout what was by then a Christianized
Greco-Roman world by the
6th century.
[6]"
This would indicate to me that all the original Christian manuscripts were almost certainly in scroll format.