I dont know of any specific plans for scratchbuilding a roundhouse but I have come across some prototype drawings at various places on the web. Alot depends on what era and size. There were many different designs. I have seen drawings for early covered roundhouses at martinsburg Wva. and some drawings for an Erie roundhouse I may be able to find. Is this a modern design or an early structure? What is the largest engine that needs to go inside?

Search This website for the whole series on scratchbuilding a roundhouse by Les Halmos. Great stuff!!

Besides MR, RMC, if you search for "HABS-HAER" that will bring you to the Library of Congress site.

Search there for "roundhouse" and you will find lots of pictures and some plans for various roundhouses.  I know at least one set of plans is in there since they have plans available for the Wilmington & Northern, Reading Co., roundhouse at Wilmington, DE.

Saw this thread and I've checked out the link you posted. Just the listing under R was overwhelming. Lots of great stuff!

I've looked at the American Memory pages before for photos...Didn't realize they had drawings.

Frank Musick