After sawing off the roof I had to square off the top edge of the walls. I suppose there's an easy way to do that, but I did it by cutting the walls apart at the corners, then pressing them against a sheet of sandpaper and gently sanding away the bumps until I had a smooth edge. When the top edges both looked nice and straight, I got ready to glue them back to the floor ...

But first, I cut away a thick plastic flange along either side of the floor that used to help hold the shell on. Didn't need that any longer. I also cut a piece of sheet styrene and glued that over the floor to make for a clean, flat working surface.

Finally, I glued the sides back in place. When I checked this morning, the glue had set up firm and tight.

I didn't have enough time to day to do much more than think about how I wanted to arrange the interior, although I did cut and paste together some card paper strips to rough out the rooms I wanted.