The change of ownership process on property is called conveyancing; this applies to both land and house. Once you have completed the build, you will need to ensure you have a number of documents in hand in case you do go to sell. There may be tax liabilities in ROI, and stamp duty due in both NI and ROI. 

By law in both NI and ROI you need a building energy rating before moving in, even if you built your house yourself to live in. You will need some form of certificate of compliance with the building regulations (from building control in NI or your certifier in ROI) AND a certificate that you complied with the planning conditions (from your certifier)Remember that a build must usually start within five years of planning having been granted.