Surprisingly I still have a few unused mushroom tops that I made a few years ago. So, I made a cardboard cylinder. Covered with wallpaper lining paper and then kitchen roll. I also made a fake brick chimney stack. That was just a simple cardboard shape covered with a brick print texture. It was a bit fiddly cutting the hole in the mushroom!
The door and door frame are balsa wood. I usually hot glue the wood onto a cardboard template. I then hold the door frame against the mushroom stalk and draw around it before cutting the aperture with a craft knife.
The dormer window is made from a clear yogurt pot with a balsa wood window frame. I then pulled apart a pine cone and hot glued the kernels to make roofing tiles.