Plastic owls are a waste in my experience....targeted bird ends up using the "owl" as a roost. <G>
Can you block the entrances the birds use to get into the building? some chickenwire or something?
An eagle cost me $500 bucks this spring -- he took the prop off my masthead anemometer.
We should of made the turkey the national symbol, then we could shoot eagles. 
it'd be pretty hard for me to get up there. besides, there's enough nooks and crannys on top of the roof, that they'd just move up there. that's why i'm trying to find somethign to chase em away.
i'm honestly not totally averse to killing them, but i'd rather not have to do that. i just want em to go away. if i have to kill a few dozen of em to make that happen, then i will. i've read about a poison that kills them slowly, so that the affected birds cry in agony. this cry scares the rest away, and once they're broken of that habit, then it's settled. but once again......i don't like the idea of killing anything slowly.
if it were as simple as the noises, i could load the proper sounds on a usb stick, and either play them through my computer, or leave the windows down on my car, and play those sounds through the cars stereo.
i figured we've got a very large, very knowledgeable community here, and for something like this it's a good place to start.