*Full credit for this build goes to EpicNameBro (http://www.youtube.com/user/epicnamebro)
This build focuses on the use of two main buffs: Crystal Magic Weapon and Power Within. The stats you will be primarily focusing on for this build is Dexterity, Intelligence and Endurance. The class you start as is up to you, however, I found the Warrior to fit my needs the best. Choose the Master Key as your gift.
The final build should look something like this:
First, you want to level up your strength to 16 to to be able to wield both the Eagle Crest Shield, Black Knight Shield and the Drake Sword (Drake sword is used for early New Game only). After that, focus on getting your Vitality and Endurance to 20 respectively. Then, put points into Endurance, Dexterity and Intelligence evenly up to 40. The reason we stop at 40 is that diminishing returns make it not worth it to spend further points into that stat. After that you can pump all the rest of the points into Vitality.
The Eagle Crest shield has the lowest strength requirements of any greatshield in the game and also has amazing Stability, which makes it an ideal candidate for this low-strength setup. The Black Knight shield also has the low requirement of 16 strength, but has the drawback of not having as much Stability as the Eagle Crest Shield. This shield is for situations when you need to parry, such as the fight against Gwyn (Note: The fire resistance also makes it amazing against Gwyn). One thing to note is that you should upgrade the Eagle Crest Shield to +14, and not 15 as you don't gain any extra stability or defense of note, and you should save your Titanite Slab from your first playthrough for upgrading a weapon.
As for the weapons you should use, the one I use mainly is the Balder Side Sword+15 as it scales well with Dexterity, is fast and has a good move set. You can also roll with Ricard's Rapier as it's 2h R2 attack is devastating.
The Catalyst you use depends on the Intelligence you are currently at. For Int levels below 30, Oolacile Ivory Catalyst has the best magic adjust in the game for that level, but doesn't scale after that. At 32 you have the option of using the Tin Crystallization Catalyst, however this halves the number of casts you can do. From the 30 - 48 I recommend the Sorcerer's Catalyst. If you decide to go past 40 Int, at 48 Logan's Catalyst becomes the best one in the game.
For rings, use the Ring of Favor and Protection and the Lingering Dragoncrest ring (for bosses) and the Darkwood Grain Ring for everything else. The Lingering Dragoncrest ring increases the duration of magic buffs by 50% which is amazing for this build. This also has the nice side effect of makng the HP drain from Power Within drain 100% of your HP over 150 seconds as opposed to the standard 100 seconds. This brings me to my next point, the Pyromancy Flame.
The first of your Magic Slots should filled with Power Within. To use this you need to use the Pyromancy Flame, however it is best NOT to upgrade the glove at all. This is because the 40% damage buff you get from Power Within doesn't get any stronger as you upgrade, however the HP Drain WILL get stronger. The second slot should be filled with Crystal Magic Weapon. This is the bread and butter of the build. This spell adds 1.4x your magic adjust as damage. This ontop of Power Within is borderline OP in NG+. As for your last slot, I used Homing Crystal Mass for some extra bit of damage, and also to help kill some annoying ranged enemies in the game such as the Mosquitoes in Blighttown, etc . You can choose not to use Homing Crystal Mass if you wish and only get 12 Attunement as opposed to 14.
As for Armour. This doesn't really matter all too much. You want to be keeping your weight burden under 50% and have as much poise as possible. Probably the best armour for this is the Catarina Armor. It has 55 poise and weighs 30, however it slows down stamina regen slightly. There are other good armours out there too if you'd prefer something that's a little easier on the eyes and without the downside of slow stam regen. I personally use the Brass Set, which can be found after defeating Gwyndolin and looting one of the chests behind him.
Anyway, I hope this guide was helpful. This build absolutely destroys most bosses in the game and is very fun too! Enjoy! :)
UPDATE: Since the Prepare to Die Edition, some of this information is out of date. For example the Eagle Shield has been nerfed from 100% Damage reduction to 95%. An alternative to this shield could be the Iron Round Shield. It has decent Stability, and has the deflection of a Greatshield. Another good choice is the Balder Shield.