Nycticorax Building packages and developing on Budgie (or other projects) are different things.
Packaging is quite simple it's just about reading the build instructions provided by the source and the macros makes it easier. Just check the packaging section on the help center.
Budgie development -> Check the repository.
You may have a look at this, this and of course at the repository of the applications you'd like to contribute to since each application has its own way of working.