In order for `rtcds` to find your model (the <model_name>.mdl file) the `RCG_LIB_PATH` env variable needs to have a path to the directory containing it. The best way to do that, is adding the directory path to the `RCG_LIB_PATH` line in the `/etc/advligorts/env` file.
If you have your custom model located at `/home/controls/models/` then you should add that path (colon (:) separated) to your env file.
While `rtcds` has appended some additional paths to the `RCG_LIB_PATH` variable, the path we added (`/home/controls/models/`) is present in the list. Now when we run `rtcds build <model_name>`, `rtcds` will look in `/home/controls/models/` for a file named `<model_name>.mdl`