I have, more or less, decided on what roles I envision most of the character classes playing in my setting.
Barbarian: ?
Bard: ?
Cleric: Most dwell within the protective confines of the cities. A few, however, feel an urge to go among the inhabitants of the wilderness areas. Their normal, day to day, duties include blessings and sanctification rituals, making laws, city/government administration, and conducting the liturgy in the various churches and temples to name a few things.
Druid: Druids are to the wilderness dwelling folk what clerics are to city folk. Outside the cities, druids are very useful because they are capable of turning and controlling undead plants the way clerics can undead creatures.
Fighter: For the most part, fighters make up the bulk of of the militias. They can be found in both city and wilderness areas protecting those they live among.
Monk: Few monks live within the confines of the city. Most dwell in monastaries located in the wilderness regions. They protect themselves as best they can. Sometimes certain monastaries will try and bring a cleric or druid to them.
Paladin: LG fighters who are responsible for most of the protection. They enforce the laws made by the clerics. Whenever someone leaves the city, if possible Paladins will accompany them. Generally speaking a paladin will lead armies in instances of war. A person is pre-ordained to became a Paladin at birth. They are pre-ordained by motes (shards of positive energy) , who are attracted to the purity of a persons heart. When a person is born, these motes will seek out the pure and righteous and enter the paladins body. It is this mote that is the source of a paladins pos. energy. Upon the death of a paladin, the mote will leave the deceased's body and seek out another who is pure in heart.
Ranger: A ranger functions similar to a paladin, but they are most commonly found in the wilds.
Rogue: There are severe penalties for those caught robbing and stealing. There are two solutions to this problem the rogues face, don't get caught or hire out as a guide or spy and limit stealing to enemies of the lawmakers. Rogues are also often hired to track down practitioners of necromancy. Practice of necromancy is illegal in most societies and an offense that is either jailable or punishable by death.
Sorcerer: same as PHB
Wizard: same as PHB, note however information under the rogue entry about necromancy. There are no public colleges of necromancy. Any such colleges are well hidden. Most, if not all these colleges are well outside the jurisdiction of the cities.
As I said at the beginning, this is how I picture the roles of character classes in the context of my setting. There are a few changes, but nothing too significant I think. Also still trying to come up with something for the barbarian and bard classes.