One Car Garage Converted to Living Space

[Kyle Doney]

I have a house I'm closing on next week that the owner converted the garage into a man cave type of deal. They put in a window and framed in the one car garage door (looks fine). Its carpeted, drywalled, electric, but no heat / AC. They leave the door open and it heats and cools it.  You can see the slope of the floor from the back of the garage to the front. 

What do you do: 

1) Convert back to a one car (theres no other garage). 2) Leave as is. 3) Level floor, add heat and AC, new flooring and get the 288 additional sq ft?. 

Whats the highest return in this situation?