MagicalMaster can most likely give you some sound advice on character builds
It's like the Bat Signal! Except I'm a little late.
Even got to the point where I respec'd to Sorc 1/RDD 10/Fighter 5 to finish the game
So, I'm still learning the ropes, but I'd like to know more about creating a decent character instead of copy-paste a build from the internet
Funnily enough, your build is better than I think you feared it might be. RDD is indeed melee focused and common builds include things like Bard 2(or Sorcerer, but Bard gives Tumble/UMD)/Fighter 28/RDD 10 (or something similar). The main idea is to use the large AC and Str increases from RDD make the build better than a 40 Fighter or something similar.
On the flip side, if you want to be a caster Sorcerer in a future playthrough, you should avoid RDD and basically go pure Sorcerer.
I'm going to nitpick some of Rogueknight's points in a moment, but his advice is good in general. Beyond that, we can give a lot more help if you ask for advice about a specific character type (or class or something). There are so many potential builds out there that we couldn't possibly easily cover them all here.
With only a Cha of 16 a creature's spell resistance can be a problem.
Int of 12 only gives you a total of 4 skill points at level up. You need concentration, 8 lore (if you want RDD)
search (so you don't step on a trap and get killed) , persuade ( for extra quests and loot), spellcraft gives bonus to all saving throws against spells.
search and persuade will cost you 2 skill points each. that means that you will step on a trap or fail to get a quest or extra loot.
A few things...
A, Charisma has nothing to do with spell resistance. Charisma will give you more spells per day, make it harder for an enemy to make the Fortitude/Reflex/Will save for a spell, boost some Charisma skills, and in some modules make people like you more...but it won't help penetrate spell resistance.
B, int of 12 gives you *three* skill points. 2 from Sorcerer, 1 from Intelligence modifier of 1. The *fourth* skill point came from being Human.
C, Search isn't worth it for a Sorcerer. You can't get enough points to detect difficult traps after a few levels anyway and you need rogue levels to detect the worst traps on top of that.
My Sorcerer started at lv1
Str 8(-1)
Dex 10(+0)
Con 10(+0)
Wis 8(-1)
Int 16(+3)
Cha 18(+4)
The 16 Int is my choice I want 6 skill points at level up.
I'd go with
Str 8
Dex 8
Con 14
Int 14
Wis 10
Cha 18
or
Str 8
Dex 8
Con 16
Int 12
Wis 8
Cha 18
The latter trades off 1 skill point per level for 1 more HP per level and 1 more Fortitude. I usually go Concentration, Persuasion, Spellcraft, and Tumble with four points per level.
2) Do not forget about the Tumble skill. Every 5 points in this increases your AC by 1, which can ultimately add up to very significant AC bonuses. Increase it even as a cross-class skill as necessary. In qualification of 1), above, it can even be worth putting extra points in Intelligence just to have enough skill points to max out Tumble.
For Wizards/Sorcerers, "typical" builds will have such low AC that Tumble isn't taken for the AC boost but rather for the ability to move through combat without triggering AoOs.
3) Multi-classes are better than single classes. There are many classes that can add significant benefits even if you only take a few levels in them, e.g. only 3 levels of Rogue gives you Evasion (allowing you to avoid damage from many spells), Uncanny Dodge (AC boost in some situations), 2d6 Sneak Attack Damage, and lots of extra skill points, only 4 levels of Fighter gives you proficiency in every Armor & non-Exotic weapon, 3 extra feats, and access to the Weapon Specialization feat, 1-3 levels of Paladin can add significant bonuses to a Sorcerer or other class with high charisma, etc.
Many players view some/all of this behavior as abusing or "cheesing" the game -- a level 30 Sorcerer suddenly taking 1 level of Paladin and gaining +15 to all saving throws does not make much sense. Quite a few Persistent Worlds will either have rules prohibiting/limiting this behavior and/or modify the rules to make it less appealing.
Most single player modules (technically 100% of the ones I've played) also assume you *aren't* abusing those quirks of the game and are designed around more "standard" characters -- pure classes or more evenly split classes (40 Rogue cool, 40 Fighter cool, 20 Rogue/20 Fighter cool, 36 Fighter/4 Rogue what?).
4) When multi-classing, pay attention to the net Base Attack Bonus. You need a BAB of at least 16 to get the full 4 attacks per round. E.g. 16 levels in a medium BAB class & 4 in a high BAB class (adding up to a BAB of 16) would do better than 17 & 3, respectively (adding up to a BAB of 15).
How relevant this advice is will depend on several things.
A, a level 20 (or under) world/campaign versus a 21+ world/campaign. A 17 Druid/3 Fighter is going to be better than a 16 Druid/4 Fighter due to getting access to level 9 spells. And a campaign that will end before level 20 makes it irrelevant.
B, if you're a Cleric. Clerics actually *want* to hit 15 BAB and *not* 16 BAB due to how a specific buff works.
C, if it hurts you elsewhere tremendously for some reason. The 1 AB actually matters more than the extra attack (remember that the 4th attack is made at a -15 penalty -- so even if you hit your target 80% of the time on your first attack you're going to hit only 5% of that time on the fourth attack) -- not worth giving up 2 AB from class skills or feats or something (if that somehow happens) *just* for the fourth attack. Which also means that going up to 17+ BAB is very helpful if you can do it. 16 isn't really a magical number.
Also keep in mind that there is more to NWN than simply having a strong build. That certainly helps, but expert players can handily beat the OC even with a very sub-optimal build.
This can be split into a *minimum* of two main parts (there's really a lot more): gear and knowledge.
A physical attacker (Fighter, Rogue, Arcane Archer, etc) is going to heavily depend on using the correct gear for AC, AB, immunities, resistances, etc. You're mostly going to be auto-attacking and you are very gear dependent.
A spellcaster is going to heavily depend on using the correct *spells.* You could beat the OC naked with a Sorcerer. Not the case with a Fighter (now a Monk with bonuses to unarmed maybe). Knowing *what* to cast will matter far more than what you are wearing. Much less gear dependent.
