Building a detached garage with apartment

[Ben Howard]

Hi my name is Ben. I live in Nashville, TN and am looking to build a detached 2 garage with 2/1 apartment above. I personally went down to Metro to get a building permit because I wanted to make sure what I wanted to do was even feasible for our property, zoning restrictions, etc. Prior to getting the building permit, I had the lot surveyed and site plan drawn up. Before starting the project I talked to a few general contractors that said the type of building I am looking for 25x25 detached garage would be $50K to build. Our plan is 24x24. We are in talks but still looking for a contractor. The project should be funded my early next week as we closed on the loan this week. 

For the numbers on the deal, the loan is costing an additional $235 for a total mortgage/taxes/insurance/etc number of $1120 for $55k in cash. I believe the rental value for the property including a two car garage is in the $1400-$1600 range. 

I'm looking for any knowledge or experience you can impart on a project like this, if you know a contractor that would be good, anything. Thanks in advance!!