ldap field relationship

Hello community.

I'm still not sure how to fillup the ldap fields in a way that also SDP works automatical with the right information. We're a small company with only one central and one branch office both located within the same city. Within these locations we're having some offices (rooms). Overall we have just 5 departments.

So I thought it would be a hierarchy like that:

SDP Regions        == have only one. The City. (What, if we expand and have branch offices in other citys / countrys?)
SDP Sites            == we got 2: Our central and branch office.
SDP Departments == our 5 departments
???                      == rooms, the employees sit in

But on the other handside we have a php script to create a phonelist from the ldap. This script graps the ldap-field office (physicaldeliveryofficename) as the office (or better room-) number of the employees.

I'm quite confused about the terms and their use now. Actually SDP gets the offices as sites. Now I'd like to know how to resolv this:
1. Have SDP working and using the hierarchy described above
2. Have the php-script working with the correct room numbers (as it is now)
3. Have information about which room the ticket opener sits in within the system (room number)

Any clarification about these basics would be appreciated. I found some threads but still I'm confused (maybe more than before reading).

Regards,
Ronald