what document's a need for permanent resident of USA to travel to turkey?

Visa and passport, at a minimum. Look at the webpages below for more info. The best source of info though would be your country of citizenship's embassy in the US.

Depends on your acutal & valid passport.

Your USA green card helps you get the visa in USA but doesn't signify much when you are on Turkish customs.

A valid passport and buy your visa at the airport. About 100.00 USD last I heard. Visa is good for three months.

Visa.If you are going to be there for less than 30 days get the 30 day Visa.The longer the stay on the Visa,the more they will charge you.Its best if you get the Visa before you go,because altho I love Turkey,go every year,and work for a Turkish company,they can try to rip you off when you get there.