I came up with a (highly questionable) min-max build which deprived can do at a slightly lower SL than any other class. The stats to max are endurance, intelligence and faith. To prevent any other class from matching your stats, the following limits must be imposed:
* 11-13 vitality (+0-2 levels; +0-1 if attunement is not leveled)
* 11, 12, or 14 attunement (+0, 1 or 3 levels; +3 recommended)
* 11 strength (don't level it at all)
* 11-13 dexterity (+0-2 levels; at least 1 level is required for this build, while 2 levels is kind of useless)
At the start of the game, level dexterity once, then go to New Londo Ruins. Pick up the composite bow (the estoc can also be used). A little later on, you can switch to two-handing a halberd. A few levels can be used to get up to two extra attunement slots, and maybe a tiny amount of HP as well. After that, the only stats to level are endurance, faith, and intelligence. In the late game, acquire the greatsword of Artorias. You won't meet the strength or dexterity requirements, but it still should do lots of magic damage. However, the extremely clunky swing animation probably limits its use to falling attacks and maybe backstabs. Finally, by the end of the game, you'll most likely end up having to go over the soft cap of a stat. I recommend going over the cap of endurance and getting as much armor as possible while keeping a light roll. You'll still die easily, but you can maybe get enough poise to take some hits without flinching.
If anyone wants to try this build, I'm curious to hear if and how well it works.