One thing I like about the RCPE railroad is that it is one of the few that still uses a turntable to store and turn it's engines, despite being 2017!
The turntable in Huron South Dakota is on the National Register of Historical places and gets plenty of active use, so it probably won't be tore up any time soon. In addition to the turntable, part of the roundhouse is still used even though it was built back in the early 1900's. However, the roundhouse doesn't have a tall enough ceiling for pulling large pieces off of the SD40 fleet, so beside the roundhouse also exists a machine shop and fuel/sanding area.
Now then, this plan is merely a rough draft and therefore isn't an accurate replica of the roundhouse area, but something like this layout could be used to house and store a number of SD40-2 locomotives. If wanting to build a fleet, this is probably the best way to run the engines without having a proper train layout.