I can hear you already - "Wait..spells? On a Faith Build!?" Well, the trick to this is to get the minimum 10 Magic required for getting these spells from Sage Freke, and then getting Soulsucked or deleveling yourself until Magic returns to the base value of 6.
Warding (Excellent alternative to SC, low MP cost and instant casting. If your SC gets cracked, you are going to want and need this to survive.)
Poison Cloud(Great for added versatility and in drawn-out battles)
Death Cloud(If for some reason you don't want to use Warding)
Any other spell you have a spare Demon Soul for.
50 Vitality should be fairly obvious. As this build only really pours points into two other stats, you'll find yourself with plenty to spare leading up to SL 120. If you like, you can drop 3 points from it and be exactly on SL 120.
The 18 Intelligence is one of the areas where this build differs from the standardised 'Cookie Cutter' Faith builds in favour of increased versatility. I personally prefer the extra spell slot to allow use of Poison Cloud and Warding, and since you'll be getting 15 Int anyway to use Second Chance, another 3 points when you have little else to put them into to reach the desired PvP level won't hurt.
40 Endurance really shouldn't need explanation. For the sake of argument, getting 40 End is standard for all melee PvP builds, and should be for all PvE builds as well. You reach the Stamina cap (160), and get a decent bit of equip weight and other things thrown in as bonus.
20 Strength is another variation area. In brief, I favour 20 Str for the use of a Guillotine Axe, as a few people on here who I have duelled will tell you - it is deadly.
12 Dexterity is base, it's not necessary to increase it.
Magic should be increased to 10 and then deleveled back to 6 to save 4 SLs. (See above)
50 Faith is the maximum I would ever advise, given that the diminishing returns afterwards are punishing.