Need help with Postfix package creation

[Buzai Andras]

Hi all,

I am not sure if this is the place to ask help for my problem but I'll
try my luck :).
What I am trying to do is to build a .deb package for Postfix 2.8 that
will be used in my local network (on Ubuntu 10.04 LTS servers).
I would like the .deb installation to be as close as possible to the
way Postfix is installed directly from source (with as few
modifications to the upstream source as possible).
I consulted the documentation related to package building from the
Ubuntu wiki and also the Debian New Maintainers' guide.

I tried to build it the following way:
1. dh_make -s -c gpl
2. edited the debian/control file
3. I created the source package with: debuild -S -sa
4. I run: sudo pbuilder build *.dsc.

The problem is that when pbuilder executes the postfix-install script
I get errors with permission denied for creating directories (since
there is no root access).

What am I doing wrong? Where? :)
What should be the approach for doing what I am trying to do?
Any help is greatly appreciated.

Best regards,

Buzai Andras