So two important structures other than the roundhouse that I needed to visualize are the freight station and the enormous water tower/tank that loomed over the station and section house. Ron Pleis article in RMC indicated the water tank was 45 feet in diameter. However it was on a low wood platform (not steel) only about 14 feet high as it was also up a bit on the slope of the hill to the west of downtown Port Costa. The mock up is just some cardboard bent to form a 45 foot diameter tank. I covered it badly with black duct tape as it was on hand to give it the right coloration. It's mounted on blocks of wood and granite counter samples to approximate the height. I don't know if I will model the water treatment building(s?) behind the section house on some sort of angle where the very square corner of the two sections of the layout now join.
The backside of the freight station (the freight house is the smaller building next door) does not show up in most pictures of the station area. There was one tantalizing view from an angle in Ron's RMC article. Ron attributes the picture to Bob Morris, but Bob has indicated to me that he does not have that picture. Because my layout is viewed looking north over the Carquinez Straits the backside of the station building will be highly visible. Anyway I analyzed that picture for window and door locations and made an assumption that the windows and doors were the same size as on the well documented track side. The mockup below is some cardboard covered with yellow frog masking tape with unpainted Tichy doors and windows tacked to it in the locations I guessed at. The freight door is scratch built and a test bed for SP freight freight house trim brown. The small 4 pane window is too large and will be replaced.
Note: I recently found a picture of the backside of the station building on the Contra Costa County Historical website. The backside of the building visible above will change shortly.