This site has several thousand pages of useful plans and illustrations on how to build various items used around the farm. Some are quite outdated and some are timeless. But it's interesting to see what were considered handy and time saving devices 100 years ago.
http://journeytoforever.org/farm_library/device/devicesToC.html#contents
http://journeytoforever.org/farm_library/device/devicesToC.html#contents