Everyone gets access to 4 roles (builds) they can swap through on the fly. Your roles can use completely different classes so there's a lot of room for flexibility.
I'm a mage, and currently my main is a Necromancer/Warlock/Chloromancer which is a pretty standard necro focused build with 2 points in chloro for the healing DoT and radiant spores. I also have a Necro/Lock/Dom spec for when doing dungeons and the group wants me to take CC or for when I occasionally do some pvp. For my other two builds I'm planning to have a chloromancer focused build in case I need to heal (even though as necro I can already heal a little) and either a pyromancer or stormcaller based direct damage build.
What kind of roles are you guys planning to use in your 4 role slots? Any suggestions for what kind of roles people should have to switch to?