There isn't necessarily any set way to define a Ruby project. But, generally RubyGems have this file structure:
.
├── bin
│ └── mygem
├── Gemfile
├── lib
│ ├── mygem
│ │ └── version.rb
│ └── mygem.rb
├── LICENSE
├── mygem.gemspec
├── Rakefile
└── README.md
Of course, there is also other directories and files in the project root, for tests, .ruby-version
, etc.