I need a vent for a 9 x 9 building with a washer/dryer/freezer in it.
And should it have a thermostat?
You need an exhaust fan, very small exhaust fan, because the building is small 9' x 9' It will be a good idea to have a thermostat to turn "on" the exhaust fan when the room is too warm, maybe over 80f. Look for an exhaust fan bathroom, like 80 cfm or 100 cfm. Get insulation for the roof, so the building doesn't get too warm or cold, the freezer can't work with a very hot 95f or cold 55f temperature. Grainger catalog has exhaust bathrooms or look for one small.