what if you were to make up a were dragon?
For starters, when in hybrid form (if there is one) and in dragon form there shouldn't be and dexterity bonuses because all dragons in general have average (10) dexterity.
They should have high bunuses in strength, and probably above average bounuses to constitution. Most large dragons have 23 in strength, so the strength bonus in both hybrid and dragon form should be between 10-14. Most large dragons have 19 in constitution, so the constitution bunus in both hybrid and dragon form should be between 6-10.
Natural ac =15-18 (if you can consider this to not be to powerful)
So spell like abilities
When in hybrid form, they don't get wings. In dragon form, they should be able to fly atleast twice there movement rate with poor or better maneuverability.
Should gain all of the attack forms for a large dragon in both hybrid and dragon form.
Alignment should be based on the type of weredragon. ie. red weredragongs should be chaotic evil(duh!)
Breath weapon usage and strength, hmm... This will be an issue, because if it is based on the strength and usage of a normal dragon of that type then many may consider it to be to strong, ie. consider a PrC with an 8d10 breath weapon that can damage badies in a 40 ft. cone once every 1d4 rounds (please give suggetions)
Hopefully what I put here will inspire to create and give you guys a firm base to create a real weredragon. I will probably add on too.