I am coding a PHP serial access class and have been taking pointers from the PHP-serial class on Google Code (here). That class is based on PHP 4 and I'm creating a PHP 5 class that allows more functionality and is specific to some business demands I have.

There is no code copied and I have done all the coding. Does the class I'm writing fall under the Google Code's GPL or am I free to select a license that I feel is appropriate? I'm not sure of the standard that applies to licensing when you are only looking to another work for pointers.