Here's the roof for the tank pad in a partial state of construction:
Basically, it's a 0.040 in sheet of styrene, cut to the shape specified in the article, with a piece of fine sandpaper glued to one side to simulate roofing material. Mr. Moore recommends two things that I didn't follow: 1) giving some three-dimensional shape to the roof, and 2) covering it with thinned glue and sprinked with fine stone. I closely examined the pictures in his article and his roof looked flat, so I'm not sure if he built it as he described, or if the perspective of the photos distorted the shape of the roof. Also, I though sandpaper was easier to apply. To get the sandpaper to stick, you'll need to lightly sand the styrene sheet before coating with a thin layer of white glue. To keep the whole thing flat while it dried, I sat my 12v marine battery on top. When dried, I edged it with thin styrene angle.
Here is the test fit of the roof to make sure everything is level. The vertical posts on the tank pad are made from 3 mm, square-section styrene. Since the tanks are different from those in the article, I had to arrange the posts a little differently, but tried to keep the same overall appearance. The biggest change is that I had to have 3 posts on the back instead of two so that there will be proper support for the inter-tank elevated walkway. I must admit that getting all the posts to the correct length was an exercise in trial-and-error sanding and fitting.
The tank pad roof is painted with a thinned, loosely mixed, wash of flat black and dark gray. The tv controller made a handy weight for holding the main building roof panel in place while the glue dried. These roof panels were also cut from 0.040 in styrene.