When I rebuilt my main outside layout I included a freight yard that turned out to be in direct sunlight all day.
At the time this did not seem to be a problem but looking back I think that is the main reason I have used that freight yard very little.
On the caboose layout I built a freight shed which works fine because I can switch the cars while standing over the shed with the roof up.
Unfortunately even inside the shed (which is protected from sun and rain) I still get some rust on the metal wheels so I only put unimportant cars in that shed.
The problem with the freight yard in question is that I would like to be able to leave freight cars in it for several days at a time in good weather but have them protected from the UV of sunlight and from an occasional afternoon shower.
A shed or a roof that was not transparent would prevent me from seeing the cars inside the shed so that I could remotely move cars or trains in and out.
About the only solution that I can think of would be a raised roof that is low enough to protect the freight yard from sun and rain but high enough that I could see what is parked in the freight yard.
This may be more trouble than it is worth but perhaps someone has resolved this issue elsewhere and can share what they did.
Thanks,
Jerry