Purchasing Multiunit Property vs Self Buildout

[Edward Ruan]

So I'm looking to currently buy a small multifamily property, but was advised but someone of questionable real estate knowledge that rather than trying to purchase a multifamily upfront, it might be better to buy a single family home with excess space in the lot and eventually add a studio or extend the building on my own. What is the truth in that, how hard/expensive is it to build something like that and how does it compare to simply buying the full package? 

For reference, I live in California, in the East Bay.