The main thing I would watch out for is shadows, to ensure shadows don't suddenly get chopped off in different pictures.
Personally what I did when TC was only 32 bit, was
(1) to hide foreground stuff watching out where shadows etc. fell, render the background (in your case - walls, roof, train), and save-as a picture, did any minor alterations in a paint program (Corel in my case), I didn't remove background of create any transparent areas in Corel), I then used the picture as wrapped image onto a box or sheet, and then rendered the image and all foreground stuff for the final picture,.
(2) I did occasionally render in two halves (with a little overlap), then 'stitched' the two halves together in Corel.
Not saying they are the best ways, just what worked for me at the time.