Check out my generator shed. I got tired of listening to the generator run so I built the shed. I put an intake vent under the floor and low on the two walls facing away from the cabin. I then istalled a roof ventilator electric fan ( removed the thermostat so it runs all the time) in the roof to suck out all the exhaust and keep the room cool. I then insulated the walls with acoustical ceiling tiles. You can barely hear it running now. http://i401.photobucket.com/albums/p.../IMG001542.jpg
It is getting plenty of air. Roof Ventilator moves 1600 cubic feet per minute and is made to cool 2300 sq ft of attic space. The shed is only 112 cubic ft of space so It changes all the air in the shed every 5 seconds. It feels like a wind tunnel in the shed with the fan running.