I usually use one of the multi/basic industry tracks and place the buildings in a different layer, to avoid issues with overlapping objects. The "Multi Industry" series and the "basic industry" (BI2,BI3) series tracks are useful for a multitude of applications and most of them can be configured easily in the session part of Surveyor (i.e. edit session) by using the "?" in the "objects" tab. As I recall the "BI2" script, in the "extern" field, lets one link multiple tracks together to make one industry such that one could have separate tracks for multiple input/s or output/s in a process; i.e. two input tracks one unloading a liquid product (paint?) and one unloading a solid product (lumber?) both linked to a third outputting a third product (furniture?). In the example if one didn't input product in the queues then the output would cease once the queues emptied. This is fiddly and takes some trial and error with a lot of PATIENCE!
From your post I got the impression you are unloading from regular flatcars, however, if you are representing a lumber yard after about 1970 you will need a flat open area to unload centerbeam flats (which have to be unloaded evenly from both sides).