Ah, the artist. A sensitive soul, accompanying our band of adventurers in search of inspiration. Despite their talents lying somewhat outside the normal activities of an adventuring party, they can be surprisingly useful.
Experience: The Artist levels up at the same speed as a Thief/Rogue/Specialist/Whatever
Hit Dice: d4
Attack chance & Saves: as a Magic-User
Weapons & Armour: if your system restricts weapons & armour, then the Artist can use any weapons (and shields), but cannot wear armour.
Field Paintings: when presented with an unusual or impressive sight - which might be a strange landscape, monster, magnificent chamber in a dungeon, supernatural phenomenon, or something else - the Artist can make a painting. Doing this requires an hour of safe, uninterrupted work, during which the artist can freely access their subject. A painting can be sold to art collectors, like any other treasure (and the party gets XP for selling it). It's probably worth 500 silver for most paintings. The subject must be something unique or previously undiscovered to be worth anything; the point is that it captures the essence of something truly remarkable.
Wisdom Modifier: An artist's perceptive nature gives them an unusual insight into their surroundings. Their Wisdom modifier is treated as being +1 better.
Alertness: An artist is surprised less often than other characters (only a 1-in-6 chance), similarly to an Elf.
Mapping: If an artist is mapping for the party, then their skill at making quick sketches, measurements etc means that doing so doesn't slow them down at all; the party can move at full speed and still have an accurate map.
Equipment: Proper artist's materials cost the same amount as a thief's tools.