I've made a few more additions to the shop, though it is still very much in progress. The closer I get to finishing, the longer each step seems to take.
The first thing I did was to finish the sides of the shop with bricks. The last time I posted, I was planning to make the bricks from sandpaper. However, it took me a while to get to the hardware store, and in the mean time I discovered a bit of leftover paper clay in my supplies. Unlike my disastrous first attempt using damp paper clay, this time I rolled out the clay and let it dry to a leathery stiffness before I cut and glued the individual bricks on. This stopped the foam core from warping. I just cut the bricks by eye, without bothering to measure.
My next step was to add a copper gutter along the side of the shop. The gutter is made of card stock, and the downspout is a drinking straw. I was worried that my copper paint wouldn't stick to the plastic straw, so I coated it with a few heavy coats of primer first.