Thats the new grain drying barn, the old one is near the Beckhampton spring (which still hasn't started to flow yet this year!)
The couple who live with that new view are not very happy at all :(
10 mins before I took that photo I saw a mini rainbow at silbury :)
http://aveburytour.mysite.freeserve.com/Silbury/Photos/SilburyRainbow.jpg
PeteG