Thanks for the initial feedback... but maybe it would be best if I give you (collectively) more details. I fleshed things out more last night. The core idea is this would be a way to build new classes that are blends of the original classes.
I see that as a new, better way to multiclass. It fixes the problem that a multiclass characters spells and powers are less (even when considering it collects two classes of abilities) compared to a straight up character. For example a Monk5/Wizard5 gets only 3rd level spells but a Wizard10 gets third level spells and his caster level is 10 for #dice of damage, DCs and other spell effects. The monk's abilities are also more limited and even combined they don't seem as effective as a Monk10 or Wizard10.
So the idea is to create a new class by dropping some things from one and adding from the other. (Or perhaps adding from 2 or more classes or even building a new class from scratch.)
I have been pointed to some other point buy systems for 3.5, but those let you buy each individual ability and hit die and BAB increase at each level. I'm thinking of somethign more like the 2nd edition DMG's class creation system. But I'm also thinking one could use this to drop some abilities and add a few others at later levels. (Most GMs will want a story reason or ask the character to go through training though... although the "believability" issue is similar for normal multiclassing.
With that out of the way, I'd really like people to try to break this system. My hope is that because it is based on sets of abilities it is harder for people to abuse through min/maxing. If there are issues, maybe they can be fixed by altering values or maybe some other more fundamental change is needed or else maybe the idea needs to be scrapped.
There are Class Creation Points (CCP) for lack of a better term. Each class is balanced to have/use 1000 points.
The easiest way to multiclass/class blend is to look at the ability set(s) you want from the class that is less similar to your overall concept and note the points needed to get those ability sets(s). Then look at the class that is more similar to your overall concept and see what you can drop that doesn’t fit your concept. If you can drop enough points right off the bat, great. If not, then you’ll have to pick some things that you hoped to keep but hopefully aren’t too critical to your concept. (You or at least the GM doesn’t want to overpower the class.)
You could also combine three or more classes in a similar way or build the class from scratch.
Also note that you can get or spend some points by changing the BAB progression the class uses, number of skill points per level, armor allowed, weapons allowed, and Hit Dice. (Swapping saving throw charts doesn’t change the point values nor does switching which skills are class skills.
So with that out of the way, here are the CCP values for those common class attributes (hit die, BAB progression chart, etc.) and the point values for the ability sets of a few classes:
Basics
Hit Die: d6: 0CCP; d8: 60CCP; d10: 120CCP; d12: 180CCP;
Base Attack Bonus: Low (as Wizard): 0CCP; Medium (as Bard) 60CCP; High (as Fighter) 120CCP;
Skill Points/Level: 2: 0CCP; 4: 60CCP; 6: 120CCP; 8: 180CCP;
Armor: None: 0CCP; Light 20CCP; Light&Medium but no metal: 35 CCP; Light and Medium: 40CCP; Light, Medium and Heavy: 65; Add Shields: 15; Add Shields including tower shields: 20;
Weapons: Just a few: 0CCP; Simple: 20CCP; Simple plus a few others: 40CCP; Simple and Martial: 60CCP;
Barbarian Based Class Abilities
250CCP Rage abilities: Rage @1; Rage Power @2,4,6,8,10,12,14,16,18,20; Greater Rage @11; Indomitable Will @14; Tireless Rage @17; Mighty Rage @20
50CCP Maneuverability: Fast Movement @1; Uncanny dodge @2; Improved uncanny dodge @5
50CCP Trap Sense: Trap Sense +1 @3; Trap Sense +2 @6; Trap Sense +3 @9; Trap Sense +4 @12; Trap Sense +5 @15; Trap Sense +6 @18
175CCP Damage Reduction: Damage reduction 1/- @7; Damage reduction 2/- @10; Damage reduction 3/- @13; Damage reduction 4/- @16; Damage reduction 5/- @19
Druid Based Class Abilities
390CCP Spells as Druid
90CCP Orisons
85CCP Nature Bond
85CCP Other Nature Abilities: Nature Sense @1; Wild Empathy @1; Woodland Stride @2; Trackless Step @3; Resist Nature’s Lure @4; Venom Immunity @9; A Thousand Faces @13; Timeless body @15
120CCP Wild Shape
Rogue Based Class Abilities
160CCP Sneak Attack: 1d6 @1; 2d6 @3; 3d6 @5; 4d6 @7; 5d6 @9; 6d6 @11; 7d6 @13; 8d6 @15; 9d6 @17; 10d6 @19; Master strike @20
135CCP Trapfinding/sense: Trapfinding@1; Trap Sense +1 @3; Trap Sense +2 @6; Trap sense +3 @9; Trap Sense +4 @12; Trap Sense +5 @15; trap sense +6 @18;
75CCP Maneuverability: Evasion @2; Uncanny Dodge; Improved Uncanny Dodge @8
270CCP Rogue Talents: Rogue Talents @2,4,6,8,10,12,14,16,18,20; Advanced Talents @10
Sorcerer Based Class Abilities
510CCP Spells as a Sorcerer
100CCP Cantrips
10CCP Eschew Materials
150CCP Bloodline Powers: @1, 3, 9, 15, 20
80CCP Bloodline Feats: @7, 13, 19
130CCP Bloodline Spells: @ 3, 5, 7, 9, 11, 13, 15, 17, 19
Example: Druid with Bloodlines
So say you have a concept of a Druid that has bloodlines (perhaps celestial, elemental, fey, etc, but the specific bloodline doesn’t matter for the example.)
To gain Bloodline Powers, it will cost 150CCP, bloodline feats are 80CCP and bloodline spells are 130CCP for a total of 360CCP. To free up that many CCP, one would have to drop all the Druid’s abilities except his core spellcasting. Even if we drop the ability for this new druid to use armor of any kind the new druid would only be able to keep his spells and orisons (or spells and nature bond or spells and the “other nature abilities” set.)
Actually, that might fit one concept of a Druid/Sorcerer, but I’m hoping to retain a bit more of the Druid’s abilities. So if we try to use just the bloodline powers and spells from the Sorcerer it will cost 150+130=280CCP. Dropping the armor allowed gives us 50 points back. Dropping the nature bond ability gives another 85 points back and dropping the other nature skills gives another 85 points, for a total of 220. To get the other 60, I’d drop this new Bloodline Druid’s skill points to 2/level instead of the Druid’s 4/level. But one could also drop the BAB from medium to low to get the other 60 points.
So I'd love to know if there are particular class abilities groups that should cost more or less and what the reasoning is. Or if you feel strongly that I'm undervaluing skill points or Armor choices, that's good too. And if you can create a class with the above info that is unbalanced please show me that too.