I do/did/will again.
I've visited several lumber yards (distributor/dealer, not a lumber mill) and usually there is a spur or two that heads into a parking lot style unloading area. If you have room, then make sure that a forklift can access both sides of a freight car (like a centerbeam flat). If your yard receives dimensional lumber off of a boxcar (or some other building material) then on your second spur, you can have a loading ramp.
Buildings are usually open air metal sheds, and lumber is stacked inside (usually the better stuff). Outside, the stacks may still be wrapped in the white plastic sheeting they were kept in during transit. Have a small office building or trailer, a couple of pickups and such, and have a stack of old cross ties or two, as people sometimes get them at the lumber yard too.
I used as a starting point the Atlas lumber yard kit, and added some Walthers buildings. I need on my new design to build a couple of a more modern looking shed too.