The Auckland Council's website contains lots of information useful if you are thinking making changes to your heritage home or building. The links supplied here are only some of those available on their site, but they will provide you a way in to exploring what is available.
Most important at the moment are those relating to the Unitary Plan which will be the guiding document for planning for the next 30 years once it is ratified in 2016. The over-arching vision for the city of Auckland in set out in the document the Auckland Plan.
At present the Unitary Plan is in the "Proposed" phase , and mediation and hearings are taking place now. Devonport Heritage is a submitter on numerous topics. The independent hearings panel website has information on the progress of the plan through the hearings http://www.aupihp.govt.nz/.
More information on the proposed Unitary Plan can be obtained from the following site where there are also links to interactive maps and a guide on how to search for a property.
While the Unitary Plan goes through the hearings phase towards being adopted by Auckland Council the North Shore District Plan is the guiding document. This can be found here
You can phone the Council for advice and information: please contact the Council on 301 0101 and ask for the North Shore Planning help desk.