What you will need: (bare minimum)
- 10 attunement
- 10 intelligence
- Magic Weapon (and eventually Strong Magic Weapon)
- an appropriate weapon*
- Black Knight's shield
- a Catalyst
with 10 attunement, you can hold one spell; that spell will be Magic Weapon.
- Lingering Dragoncrest Ring
- Bellowing Dragoncrest Ring
- Oolacile Ivory Catalyst
- Gold-Rimmed armor set
- Demon Machete (recommended +15 normal)+
- Hidden Weapon*
These rings combined extend your magic weapon up to a minute, and increase the effect by 33%. The Ivory Catalyst ensures that you won't need to upgrade your intelligence while still having strong skills. The Demon Machete is an ideal weapon for this simply because of your high range of attack, and high strength modifier. Two-handing the weapon will help you to pump out even more damage. Because Strong magic weapon works via percentage of total physical damage, larger weapons allow you to get "more for your money". With this setup, it's easy to hit for ~1000 damage unblocked, and still a good 200~300 blocked (not to mention that if they block they will likely be staggered).
*Hidden weapon is a nasty way to make players think they can get much closer than they normally would. While you can't cast both on your weapon, it can be an effective way to get some surprised deaths (this works better if you hold a pyromancer's glove in your shield hand when engaging)
+You can also choose the raw path to reduce the amount of additional strength you would want to use. In this way, it's viable to two-hand the weapon only (or just switch to a different, smaller weapon) without even meeting the one-handed requisites.
So there you go; a very simple build that asks for very little stat scaling and is easily independent of your starting class.