Community design isn't primarily a feature-driven activity, but the following should be considered:
accounts - what is the process for entering the community?
roles - what levels / arenas of engagement are codified?
permissions - who can create, read, update, and delete what? It's also worth considering that not all permission rules need to be technically enforced; in some cases it's smoother to have social agreements (eg, you can fix typos, but please send comments rather than make major edits)