What is the File Structure for Multiple versions ?

Hi all,

As I failed in my first theme submission, I like to start from the beginning. Therefore I am creating 404 page templates and I have multiple versions of it.

Therefore, please let me know the file structure for it. Do I need to use separate CSS pages for it or in any other way.? Assume I am having 5 templates name as Project 01, Project 02, Project 03, Project 04, and Project 05. Currently I have separate Folders for each template.

Please let me know the way.

Thanks in advance