Avoid converted garage, they depreciate the value of a home much faster.
Converting the garage does not add to the square footage of your home. Technically it does, but does it help?
When most buyers approach a home with a converted garage their attitude changes. If the asking price of real estate increases due to a garage conversion - the house takes forever to sell, usually after many price reductions
Some Dallas suburbs have outlawed garage conversions and demand they are converted back.

Many conversions are homemade and look tacky.
Even professional garage conversions do very little for the value of the home
Be careful not to assume square footage of garage conversion equals square footage of original house design.
If more space is needed, It may be time to move to a new house, instead of destroying the original design of the house.

Heating and AC are usually always a problem with converted garages. However very few conversion look very nice and add a small increase in home value, usually nowhere near the cost of the garage conversion.