shipping options

Hi,

I'm trying to add some options to a default flat shippings but cant still find out with's files do i need to change :/

So the idea is to have flat shipping with default cost $5 and i want to add addresses to determine with's post office to send my packege.
And it should also be shown on the order wenn i get the email.

Like in this image what i made


I hope you underestand what im trying to do and im still looking and trying what files to modify.

Thanks

Maybe someone knows similar extansion and where i could download to modify it or how to create your own shipping modul from scratch so i could add something like this?
or any kinda helpfull informastsion