Should i add a garage conversion to my 3br2b rental?

[Joe McKelroy]

Hey, I'm new here. Last year I bought my first house, a 3bd 2b new construction house in an okay neighborhood (waco TX). I am about to convert the property to a rental, but I was thinking about doing a garage conversion and renting it out as another unit (normal size garage). 

Should I do that? Will it add more income for me or make it harder to rent out? 

As a rental, I know I can get 1800 per month for the house with a garage. The small garage conversion would likely rent for 600-700 per month. Though I might have to rent the main house for less if I add the garage conversion. a buddy of mine runs a construction business and he tell me he just did one for 30k. Idk but I estimate 40-50k all in including furnishing. (maybe i shouldn't furnish it?) 

Has anyone done this? any advice?