Creating a custom plugin for a PHP framework

Hello,

I've been toying with the idea of having a custom plugin for my PHP framework. The most notable changes would be to have certain variables set pre-defined when opening a file inside a certain folder. It's a simple principle but don't know where to start although I have a basic plugin created and am comfortable building the plugin using IDEA.

To start with, can someone point me in the right direction? 

Thanks

p.s. if you can build the plugin for me I would be open to offers