Building a dedicated room

We are beginning the early stages of looking at building a dedicated listening room above our garage for our 2 channel system. It looks as though we will be able to get about 500-600 SF. Those of you who have done it, or are in the profession, what initial guidelines or advise can you offer?
(other than the obvious planning for electrical) Garage is attached to a common wall and accessible through the kitchen, which will keep it nicely isolated from the rest of the house, Our HVAC system is only 5 years old and is a high efficiency unit, which will probably have the capacity to heat and cool the room. Electrical service is 200 amp and recently rewired with new breakers, panel, and trunk wire from street. It is located on the back wall of the garage so runs to the outlets can be kept short.