You could cut holes in the plywood ceiling can cover those with hardware cloth or if you've another use for the plywood take it down. It's a little pricey to cover the entire ceiling with cloth but can be difficult to secure hardware between the rafter soffits too. Since the plywood is up I'd be incline to simply skill saw a 4 to 6 inch wide vent on each side of room nearly the entire length then screw hardware over vent holes using washers to fasten it secure.
So we're on the same page, you'd be cutting perpendicular to the soffits to expose almost all the soffit bays each side of room. Say all bays but the two ends and keep the vent 6 inches from wall end to make securing the hardware easy on the flat ceiling.
Anywho, that would be adequate ventilation for winter and summer. I wouldn't use heat lamps at all and am in a colder climate than you.
So we're on the same page, you'd be cutting perpendicular to the soffits to expose almost all the soffit bays each side of room. Say all bays but the two ends and keep the vent 6 inches from wall end to make securing the hardware easy on the flat ceiling.
Anywho, that would be adequate ventilation for winter and summer. I wouldn't use heat lamps at all and am in a colder climate than you.