Duplex build vs buy

[Andrew Creel]

Interested in different opinions on building vs buying in the current RE market?

I am looking at either purchasing an existing “value add” duplex vs finding a correctly zoned vacant lot to build on. In both circumstances I would occupy one side and rent out the other. From most of my research it seems existing duplexes are priced @ $240 a sqft. This seems to be about the market rate to purchase a lot and build new! Opportunity cost while the vertical construction is being complete does give existing an advantage, but can you make up for this quickly with higher rents from new construction? 

Please give all opinions and let me know the details I have not thought out completely.