How to create Admin panel folder?

[eluser]web_developer[/eluser]
if I create Frotend and Backend seperately then every thing will become double.

2 config directory,
2 library.

--> I have to define 2 times DB settings. (For Frontend and for Admin)
--> I can't use my common function in admin as well as frontend. I have to declare in both library.

This is not the good way.