I have a little riff that both the guitarist and I think has potential, it'll fit as an intro, bridge and outro but I need some thing for the verse and chorus. It's F G C A#.
How do I know which key it's in, I think F as that's the first note.
Following from that, can I use anything in the rest of F Maj as the rest of the piece or should I just say stuff it and noodle around until I find something else that sounds good and tack it on and hope?
It'll be in about four different keys if I try that, does it matter?