Replacement sky for overcast photo

Having recently stayed at the magnificent Down Hall I wanted to take a photograph which did the house and its surroundings justice. Unfortunately it was overcast so my photos were all a bit dull. This was the best I could get:

I wanted to do two things. Remove the tissue from the front lawn and replace the sky with one more fitting. Apparently this is trivial in Photoshop, but I only had access to GIMP. So I found this well written tutorial and followed it. After about half an hour of playing around I produced the following result.

It is a little bit rough and I'm not sure the brightness/contrast of the sky matches the photo too well, but I'm pleased!