It's not ideal but if that's what your going to do, I can't stop you of course. I will just say that 4 birds is MAX and a good size aviary is almost a must and the birds should be trained so that they can fly and not be cooped up in a box 24/7.well, im building the loft 3x3x5 because that seems just about the max room i can have i also was going to have a decent size aviary thought.
Actually...the rule of thumb is 2 square feet per bird, minimum.The rule of thumb is 1 square foot per bird. 3x3 would mean 9 birds. assuming the third measurement(height) isn't just 1 foot. but I would say 3x3x5 is plenty of room for 4 birds. Enjoy your birds and watch out for the predators.