I tested this on Blender 2.61 as soon as I saw it on Blendernation despite the decision I had made to stay away from work a few days and tidy up the house before New Year.

Blender Window Generator Script from DragonLEE on Vimeo.

Seems to work well and I was astonished such a tool can pop up just like that… Santa must have something to do with it 😉

The settings are named in Turkish but not difficult to figure them out. I will not complain for a small detail if I get a good archviz modeling tool 🙂
The parameter editing as expected disappears as soon as you deselect the object – that is how Blender parametric objects work right now.
I saw another similar addon for creating arched openings on DragonLee vimeo account but couldn’t find a link to the script. I’ll look into it tomorrow, I really hope this will be available too 🙂

Later edit: this works no more in Blender 2.63.. sigh. Hope it will receive an update.