Because the prototype building is up on a hill, its foundation is visible in some of the photos I have found. I fabricated mine out of styrene sheet, and then reinforced the corners and the long straight.
I painted it with POLLY Scale "Milwaukee Road Gray". In the photo you can see that I installed four tabs to make sure that the foundation lines up perfectly with the rest of the building.
After I glued the foundation to the building (using superglue), I came back and used Aleene's Tacky Glue as a caulk to make sure no light gets through the gap. I used left over pieces of plastic from N-scale buildings as the tabs.
With the foundation attached, I could trim the drain pipes to match the bottom of the foundation. In this photo, the foundation still needs to be trimmed flush with the back of the building, so that the whole thing sits flush against the layout's backdrop.
I then used POLLY Scale "Reefer White" to paint the drain pipes. It seemed to be a perfect match to the white spray paint I had used on the building. I jumped the gun a bit on the painting of the main building; I should have done the gutter and drain pipe before doing the roof and the foundation, so that the whole thing could have been painted with the spray can. Oh well; it came out well anyway.
I painted the glue with which I filled the gap between the building and the foundation with some black paint, because I could see through the gap, if there was any light behind it. The building is going to be flush up against my backdrop, but it is better to be safe than sorry. The next step was to cut some pieces of clear plastic for the windows, which were glued with Formula 560 canopy glue, just in case any of it was visible later.