First, you must put a Pokémon Ruby 1.0 (US) ROM in the root directory of the repository and name it `baserom.gba`. It should have a SHA1 checksum of `f28b6ffc97847e94a6c21a63cacf633ee5c8df1e`. Then, follow the OS-specific instructions below.
Make sure that there is an environment variable called DEVKITARM with the path of the directory before the "bin" directory containing "arm-none-eabi-as", "arm-none-eabi-cpp", "arm-none-eabi-ld" and "arm-none-eabi-objcopy".
Then get the compiled tools from https://github.com/YamaArashi/pokeruby-tools. Copy the `tools/` folder over the `tools/` folder in your pokeruby directory.
When you simply enter `make` and don't specify a target, then Pokémon Ruby 1.0 will be built. However, Sapphire can also be built, along with revisions 1 and 2 of both Ruby and Sapphire. Here is a listing of each ROM that can be made, along with the command to make the ROM.
Pokémon Ruby 1.0
make ruby
Pokémon Ruby 1.1
make ruby_rev1
Pokémon Ruby 1.2
make ruby_rev2
Pokémon Sapphire 1.0
make sapphire
Pokémon Sapphire 1.1
make sapphire_rev1
Pokémon Sapphire 1.2
make sapphire_rev2
Note that if you have already built a ROM, you must run `make tidy` before building a different one. This command will delete the ROM you built as well as intermediate files, so you should copy the ROM to another directory before running `make tidy` if you would like to keep the ROM.