i would like to build a petition for a 'replica' of John Allens' roundhouse in plastic in HO scale. Fine Scale Miniatures did a replica but who can afford the price tag if you can find a kit available not to mention the time to build it
You might try a Google search for :
build John Allen G & D roundhouse
I found a fair amount of info from some links but did not look to close. You may find photos and maybe some info from discussions.
You might also try the Kalmbach forums as there are many more people there with many different types of model railroad forums than here. You migh be able to come back here and share about this issue.
Rich