@wez130 - essentially yes, they are long exposures to get the movement in the clouds, although on a couple it was too still a day to get much cloud movement without having to expose for hours, so they've had a bit of help with photoshop! The one from Malta is a blend of 2 exposures, one long and one "normal" so that the cloud reflections are still, but the clouds in the sky have movement.
I tend to create selections in photoshop so I can have some fine adjustment over different sections of the buildings using camera raw or use silver fx to process parts of the buildings without affecting the sky.
If you google fine art architecture photography you'll find a couple of good tutorials.
It's a "style" of photography I really enjoy and one I am still very much developing my skills in!