Subscribe to whatever method is being executed

In my app I'm creating an auditing package that obtains various information, one such type of information should provide different information regarding what method is executed (time it took to execute, method name, method class, assembly, etc).

I'm not looking to use an existing package or framework, but to create my own.

I can imagine that this is a complicated thing to do, but I'm looking for some pointers to get me started .