in oblivion, God-mode is not really possible, due the fact that all monsters around you level at the same rate you do.. in fact they level a little faster, making the game harder and harder to play while you level.
You ask for the best build, well let me start explaning some things for starters :
*endurance is an important stat, it will determine how much your health will grow at level up, all of the other stats have static effects, but the effect of endurance is cummulative, start with it higher and you will forever have more health than other chars.
*every race has certain powers and weaknesses, you want a race with not to much of either of them to be balanced
*some races are more liked than others, conversation with NPC is harder with some races, you want a race that is somewhat universal liked.
*Males and Females of races have different atributes.. picking your gender is not trivial.
This added up I'd advise you to play as an MALE Nord, MALE/FEMALE Redguard or MALE/FEMALE OrkThey all have +10 endurance so thats good.
they differ a bit, but not so much you cannot pick the one you like more.
Redguards are the best I'd say, they start with 5 more merchantile, and thats one of the hardest stats in the game to level.
also long term, they have TWO resistances of 75% where the other 2 have only 1,
A male redguard starts with some extra strenght, but less personality than a female making talking to npc's harder, but able you to fight at start a little better, and carry a little more
A Female redguard starts without this, and will be more easy to talk with people but less able to carry stuff.
Next you want to know your main stats :
1 ENDURANCE (I already explained you why)
2 LUCKLuck while not an essential skill, does affect gameplay, basicly every +5 luck is +2 to every skill effectivly. however it can only be leveled +1 per leveling, where the other skils can be level +10.
I'd say starting with +10 luck is more valuable, for that reason.
next you want your skills, let me explain again some things about how it works in this game :
*after a certain amound of MAYOR skill increases, you will be able to level up.
*when you level up, your health will be increased determined by your present endurance, and after that you will be allowed to add to 3 stats.
for luck, you always can only pick +1
but for all other stats you can get as high as +5!
this is determined by the total levelups of the skills suiting that stat,
Strenght for example, is linked to blunt, sharp and hand to hand.
for every 2 leveles you gained in either one of these three, your counter for strenght will go up a nothc.
so :
0-3 skill increases = +1 to strenght
4-5 " = +2 to strenght
6-7 " = +3 to strenght
8-9 " = +4 to strenght
10 and more skill increases = +5 to strenght.
now here comes the catch : every 12 MAYOR skill increases will cause you to level up.
while this will not activate before you go sleep... you cannot change your "counter" after this.
What you want for this reason is mayor skills you can level controlled (skills you do not use in normal combat and such)
so you can ensure you get your maximum bonus every level.
You can also buy 5 levels of skill training every level, but only ONCE, I suggest you do this BEFORE every level up, to not waste this.
Now you know the idea... I shall say you what skills you must pick as mayors :