Seller Financing and How to do the terms

I am new to the idea of getting seller financing.  We have a scenario for a property that may be a perfect fit to try for the first time.   What happens if we buy the duplex and want to tear it down in a few years to build new?   Would we just then continue to make normal monthly payments?  The current rental income would pay the mortgage plus about $220.  Any advice on how this might look would be much appreciated.