Pros and Cons of Adding a Garage

[Laura A.]

I'm considering doing a flip of a 1960s house located near Denver. It is 2500 finished sf, and has 3b/2b, plus a mother-in-law suite. Expected (realistic) ARV is $600k. The house is great, with one exception - there is no garage. My business partner and I are debating the merits of adding a 1-car garage (that's all there is room for). It's Denver so winter weather is a consideration. All the homes in the neighborhood are custom homes and the vast majority do have garages. Storage isn't a big factor as there is a large shed and a large utility room in the house. So, my questions are:

How much smaller is my buyer pool if there is no garage?

What kind of return do I get on the cost of building the garage?

Approximately how much should I expect to spend on a new attached garage (built to a level commensurate for a $600K house)? 

All opinions are helpful as I'm really on the fence here.