As a standard rule we use 20 point buy from pathfinder system.
Races available are human from the standard book and the races presented here.
Classes are access to any book the club has access to.
Making your character.
The first thing you do is come up with a character concept and work from there.
And your focus should be one thing and one thing only!
Buy in is what makes you want to play.
Do know if you ask for the flaw dead parents, tortured soul for inherited fortune my responce will always be.
No you can not play batman, not with 20 point buy thats for damn sure,
But perhaps it maybe something you don't get to do every day or you would like to...
Perhaps your job is very mundane and bores you so you wonder what it would be like to be someone who is sick of excitement.
A rougue would be sick of excitement...
Come of think of it a half elf rougue would be sick of excitement far more than anyone else cause his between two people and...
There you go thats buy in right there.
Some choices you will make will be purely for story and others maybe mechanical advantage, in an ideal world they should be both...
Whatever the case maybe buy in should be what your looking at.
I realise I have said buy in quite a bit now.
What buy in is what makes you interested in a story, you buy in.
That is another thing to remember, this is the start of your story and you shouldn't have to have it so detailed that your just filling the last pages.
By the same note you should not be so light on detail that your 'weafer thin'
Whatever makes you interested and makes others interest is what your going for.