Channel 12 is Very Strong at your location and will be received by the U4000. However if you will like a VHF/UHF antenna then use a Winegard HD7694P antenna. You can try either antenna in the attic. If does not work well there then mount on the shed , if mounted on the shed the antenna will need reception that is not blocked by the house or other objects to the north east and south west , so get the antenna up in the air. Here are antenna mounts ,
http://www.ronard.com/909911.html ,
http://www.ronard.com/Tripods%200703/4712.html ,
http://www.ronard.com/34424560.html ,
http://www.ronard.com/ychim.html