A really great set report from Half-Blood Prince has been posted over at the Leaky Lounge which gives some insight into the sets and spills some secrets from filiming!
Because there are plenty of spoilers, you'll have to highlight the text below to read the pieces pertaining to Rupert!
At the end of our tour we watched them filming a scene [inside Weasleys Wizard Wheezes]. When you see the scene where Fred and George are talking to Ron on the stairs, he asks how much for an item, they say '5 galleons', Ron says 'but I'm your brother' and they say '10 galleons'. Well I am standing behind the stairs (out of sight) by the door! It took eight takes just for that few seconds and I was told they only complete 2 minutes of film a day.
Much, much more can be read here!