Here's a piece of history from the USDA:
http://naldc.nal.usda.gov/naldc/download.xhtml?id=CAT87208730&content=PDF
It includes basic plans for 40 different structures including cabins, shed, barns and greenhouses.
UPDATED URL: https://naldc-legacy.nal.usda.gov/naldc/download.xhtml?id=CAT87208730&content=PDF
[cool]
I hadn't seen that one, some neat ideas. There are code issues that have changed since that time to work through on some plans but a good jumping off point for a number of designs.
Bummer, just tried to download this and not getting any luck. Hopefully it's a temporary server issue that will resolve soon.
https://www.ag.ndsu.edu/extension-aben/buildingplans (https://www.ag.ndsu.edu/extension-aben/buildingplans)
Another source for old plans. Houses, sheds, barns and all kinds of agricultural buildings. Pdfs are free to download.