how to compile a dynamic extension

Hi there, I have my own extension and I need to compile it with PHP. I was able to use the automatic build system to compile it as a static module (--with-mymodule or --enable-mymodule). However, I cannot find any documentation on how to compile it as a shared module. Can anybody enlgihten me how to generate mymodule.so and how to integrate it in the PHP build system? A step by step description would be most helpful. Your help is highly appreciated. Thanks in advance. --Charmaine