Thanks Patricia, I think the problem occurred when I decided to add the plot of land around my house - I was very pleased to see the garden wall and the road in front of the house, but didn't realise you had to start with the plot or else the house would be scrambled! I found your backup files - useful thing to know about - but unfortunately the oldest one already had the problem, probably due to my frantic efforts to correct things. Selecting e.g. a 3rd level wall in the 3D view and sending it up one level (from the ground floor in the plan view) put it in the sky above the house, and I couldn't face picking out each item and then trying to figure out how to settle them all down again in their proper places. So I went back to an earlier version I'd saved under a different name, and redid the roof conversion bits. In doing so I realised I'd made the mistake of thinking that roof dimensions down the slope referred to the part of the roof, and not to the horizontal projection of it, so I've been able to make a few corrections at the same time - it's an ill wind... By the way, I can only spend time on this at weekends, hence the delay replying. Thanks again, Chris