I thought I'd try knocking up a model of the layout in SketchUp hoping that it might save me some time and that I could print off a picture from the correct angle and work over it. I was wrong about the time saving element but it was a very helpful thing to do. Once I'd knocked the model up I realised that the view I'd chosen was such an extreme, exaggerated one that to have it match the rough I'd need to tweak the depth of field on the camera in SketchUp. This distorted everything but I thought it looked okay and helped add to the feeling of being high up and that it was a large house. Anyway, here's a screencap of the model.
I printed off a blue line and worked over that, here's the final pencils. Sam's mum and dad appear to be missing from the pencils, I guess I must have drawn them on another bit of paper and added them in later on.
These are the uncorrected inks, you can see that I started to spot the black squares in the chequered pattern on the floor and then stopped. I thought I'd leave it and give myself the option to drop it in at the colour stage or even use a different colour. If I'd filled in all the dark squares it would have been a fiddlesome nightmare to separate them out in the colouring stage should I change my mind about what colour I wanted them to be. In the end I made them blue rather than black so I was very happy I didn't fill them all in.