I have an own script where the user can login and see his registered domains. i have also pdns-admin fully installed and up and running.
what i need now from you is that you change the user interface that they can manage their domains directly from there. the script/database needs to be connected with pdns-admin (which runs in the background I guess) so the users are able to setup soa,mx,ns etc. entires over the user interface.
if you have more questions, dont hesitate to contact me by pm.