DNS, SOA and NS records in a virtual hosting environment
 

Dear All,
We have a dedicated server and I have to set-up a virtual hosting environment where multiple domains will be set-up (with apache, mail servers and the rest) for my clients.
Because it is a shared-IP environment all zones will have records that will point to the shared IP.
My question is the following:
Each zone must have a SOA and a NS record (ok at least one NS...).
Must the SOA and NS record for each domain belong to the specific domain or should I set a specific domain and set up there the NS record that will be used by all the other domains.
For example: I have the domains example.com and test.com.
In their respective master zones the SOA and NS must be ns1.example.com and ns1.test.com respectively OR should I create a "central" domain mycompany.com set up there A records for ns1.mycompany.com and then use this entry in all the other domains:
e.g. test.com IN NS ns1.mycompany.com.
Is there any difference in the two approaches ? From the way I see it all domains all equivalent.

Many Thanks to all