7ft tall eh?
that should provide you with plenty of headroom for ventilation and your gonna need a door of some sort.
so you've got 12sqft of floor space
your gonna want 50-75 watts per square foot for a total of...600watts. get a switchable ballast that way you can veg and flower in the same box unless your planning on building a second chamber for veg.
also it just occured to me that if you divided your space in half you would have two, 3ft by 2ft areas for a perpetual harvest. id put cfl in one half for germination and veg and a 400watt hps for flower in the other half.
really with that much space you have lots of options