The wife and I are looking at getting our first house shortly.  The one thing that I really wanted was a rec rm so I could have my own sanctuary to drink beer, smoke cigarettes, watch movies loudly, and of course play with my guns.  Well, she found a house that she really likes, a ranch style in our price range,  but of course...no rec room.  It has a two car garage that I  thought could be remodeled into a room or a room and a one car garage.  Nothing special.  Just walls, a ceiling, flooring, a window, and duct work for heat and air.  And maybe a dry bar if I had enough money.

Do your neighbors a favor and use the garage to keep your cars in.

no basement?

I don't know what area you're living in, but the paint job on your car(s) will last a lot longer in the garage.

wish I had a garage  

Is the garage attached or detached? Brick or siding or stucco?

If attached, you are looking at about $10 grand or so.   The important thing I would look into is the capacity of your A/C.   Depending on the actual square footage you are going to add, your existing unit may not be able to heat/cool any more additional space.

Is it a parking ramp or parking garage?!

legally or illegaly?

Quoted: Is the garage attached or detached? Brick or siding or stucco? If attached, you are looking at about $10 grand or so.

I'd say that's a pretty good rough estimate. The cost largely depends on you. How fancy do you want to get? How much, if any of the work do you plan to do? etc

The important thing I would look into is the capacity of your A/C.   Depending on the actual square footage you are going to add, your existing unit may not be able to heat/cool any more additional space.

Definitely something to check.