Pat
Thank you for your reply.
Not quite that simple unfortunately, there are multiple extrusions to find and amend and classify in a very precise manner and order. Lots (far too much actually) of trial and error before I finally got it to look like the real thing. For instance, when you convert to group of course it is no longer a door in a wall, and if there is a way to convert a group to an object that can be inserted into a wall I couldn't find it. I eventually made a wall opening and put the group in that, and then it rendered properly.
This is another example of a VW tool which initially appears useful, but when you want something that matches the real world, you discover that it is severely limited and difficult - it's a one size fits all approach, then on to a new tool in time for the next upgrade. Most of us users would like some time spent on reworking these basic tools, and forget the endless rush to have a huge list of new features for the next upgrade.