We built a two story garage with attic trusses. The space has windows on the West and East end. We would like to insulate and finish the space. Would insulation and finishing make the area cool enough to use during the summer? We have a metal roof with a ridge vent and are located in Northern Wisconsin.
Probably, but "it depends".
How much insulation, how well the ventilation ABOVE the insulation works at getting the summer heat from the roof out of that space. That part is critical. You don't mention eave or soffit vents, and if you don't have them, you don't have airflow to the ridge vent.
As a small point of whatever, I have a metal-roofed building with eave and ridge venting and I honestly find the ridge venting, in particular, rather sub-optimal - I'm seriously considering retrofitting a functional cupola. The vent is there, but the small passages appear to end up far more restrictive to airflow than would be ideal.