To jhb's point about the roof colour on my GN van, it is actually somewhat darker in reality; I'll take an outdoor photo on a brighter day. You may have to wait.....
John Mayner is showing some superb wagons on his work bench ( " tales from the carriage shop"). Some are conversions, others old cast metal kits.
The above are somewhat old technology but currently available; the Alphagraphix card kits.
The one on the right is a MGWR convertible wagon. I think the idea was that the canvas centre part of the roof could be rolled back when carrying cattle.
Until Leslie McAllister started up Provincial Wagons, these were one of the very few ways of achieving a realistic Irish wagon.
They are tedious to build but the end result is reasonable but now overtaken by Provincial Wagons.