I managed to build the project by downloading the source code and running the build command.

1. Clone the repository
2. Inside the SweetHome3D folder, run `ant`

You must have the `ant` build tool installed. Homebrew has this.
You can take a look into the "build.xml" files to see how the tool is built.

There are ".project" files which instruct your IDE on how to setup the project. I develop in Vim, so my case is a bit different. But ".project" gets you enough mileage.