Nigga = Man/Dude/Person
Nigger =

you know
Examples:
Crooked Ass Nigga
"My
nigga 2Pac, got the fuckin Glock cocked"
"My
man 2Pac, got the fuckin Glock cocked"
How Long Will They Mourn Me
"
Niggas cried to mourn a homies homicide"
"
People cried to mourn a homies homicide"
This Life I Lead
"I'll send that ass straight to God (what you doing
nigga?)"
"I'll send that ass straight to God (what you doing
man?)"
U Can Be Touched
"Life. What the fuck is life when
niggas like us.."
"Life. What the fuck is life when
dudes like us.."
I've heard rappers like Raekwon say "white niggas" before. And we all know that this term is impossible because there are no such things as "white niggas". What Raekwon actually meant was "white people". There is absolutely no problem with using "nigga" as long as you mean "man/dude/person" by it. Take a look at non-black rappers that use this word: Immortal Technique, Paul Wall, Fat Joe, etc.