Above Garage Apartment as 2nd deal

[Robert Blake]

I bought my first investment property back in November 2017. It's a live in duplex and I rent out one of the units and do AirBNB out of the finished basement. Everything is going great so far and I've been looking into doing my next deal.

In Chicago, the market can be very expensive and I was considering tearing down my detached garage and rebuilding it with an apartment above the garage. I think this could be done for less than 100k and would likely yield at least a 800sqft studio which should bring in about $900/mo in my market. I may even consider doing an AirBNB out of this unit (my current AirBNB is yielding anywhere from $950-$1500/mo). 

Am I missing anything here? Is there something I'm not considering? Is a new garage w/ apartment (and running plumbing, sewer, electric, etc) going to cost me a lot more than 100k?

I was just thinking mainly that I may be able to do my next rental deal quicker if I get a construction loan for a property that I already own.