laser cutters are very inexpensive and accessible nowadays. Once somebody published a device, producing such a set of acrylic sheets with holes is not a problem at all.
hmm.. you could use solar energy to heat the air coming through, otherwise the building would cool down right?
Also is it possible to let the air pass through into one direction only? I think strategically placing incoming/outgoing air-pass through windows, could make a decent air-flow (+heating) system.