Thank you for all your feed back. After reading through peoples thoughts I have rethought my original ideas. At the moment I am thinking of using something along the following lines:
1) I am planning to use 3d6 instead of d20 for all checks.
2) To attack a character rolls 3d6+Strength Modifier + Proficiency Modifier (Using a light weapon that the character is proficient in allows them to substitute their strength modifier for their dexterity modifier if it is higher).
3) Compare the characters modified attack roll to the difficulty (DC) to hit the target. This DC is 10 + Dexterity Modifier + Proficiency Modifier (Only add targets proficiency modifier if they are proficient in Dexterity checks OR Proficient with, and holding, a weapon that can be used to parry)
4) If the modified to hit roll is higher than the DC needed to hit the target damage is applied. Damage is 1d6 (Use the results of one of the 3d6 rolled depending on if the weapon is light, medium or heavy – See below) + Weapon Modifier + Strength Modifier (Using a light weapon that the character is proficient in allows them to substitute their strength modifier for their dexterity modifier if it is higher), (Using a weapon two handed allows a character to apply twice their strength modifier), (The bonus damage applied from strength, or dexterity, cannot exceed the base damage done from the 1d6 roll + the Weapons Damage Modifier).
5) If the target is wearing armour the damage they take is reduced by their damage reduction before it is applied.
Changes to Equipment:
Weapons are divided into three groups:
Light: These have all the properties of light and Finesse weapons. A character with proficiency in a light weapon can apply their dexterity ability modifier to hit and damage instead of their strength. A character can wield a light weapon in their “off” hand instead of a shield. Unless otherwise noted a successful hit with a light weapon dose damage equal to the lowest of the 3d6s rolled to hit.
Medium: These have all the properties of a versatile weapon. A character can use them one or two handed. If they are used two handed a character can apply twice their strength bonus to damage with medium weapons. Unless otherwise noted a successful hit with a medium weapon dose damage equal to the middle of the 3d6s rolled to hit.
Heavy: Heavy Weapons are larger than most other weapons. A medium sized character must use two hands to wield a heavy weapon (a large or larger character can wield a heavy weapon in one hand). A small character (a gnome or Halfling) cannot use a heavy weapon. If they are used two handed a character can apply twice their strength bonus to damage with heavy weapons. Unless otherwise noted a successful hit with a heavy weapon dose damage equal to the highest of the 3d6s rolled to hit.
Examples of Individual Weapon Properties:
Unarmed: light, -1 damage
Dagger: light
Rapier: light, +1 damage
Board Sword: medium, +1 damage
Great Sword: heavy, +3 damage
Armour Provided Damage Reduction:
Armour does not increase AC. Instead it reduces the amount of incoming damage from each blow by a certain amount.
Armour
Light
Padded: DR1
Leather: DR1
Hide: DR2
Medium
Brigandine: DR2
Chain Mail: DR3
Scale Mail: DR3
Heavy
Half-Plate: DR3
Banded Mail: DR4
Plate Mail: DR5
I am still a little unsure about weapon damage in this variant as it would be pretty disappointing to roll 1, 6, and 6 and only do 1 point of damage because you where using a light weapon. An alternative would be to have a light weapon do 1d6 damage and pick the best of the 3 rolls (this results in 6 about 40% of the time). Medium weapon would do 2d6 damage pick the best 2 of the 3 rolls and heavy weapon would do 3d6 damage equal to the roll (this results in 10-11 25% of the time).
can anyone suggest any further tweaking?