I've a green card I traveled out of u.s for 11 months,can I come back to u.s? And howlong can I stay inside u.s so I can travel again?

Re-enter as soon as possible before 1 year out and be ready to explain why you are out so long and your ties to the US.

For leaving, again, no time required in the US, but the shorter the time, the more difficult your subsequent re-entry to the US as the CBP inspections officer sees your travel history and it looks more like you are living outside the US and only visiting here. Good luck.

Thanks a lot,
Can you tell me we they put in the mannual of immigration that a person can stay up to one year if that will cause trouble and need a strong justifiacations?