This is a picture I found on http://www.jrwhipple.com/sr/soldehydrate.html
It is pretty self explanatory. I would just add that the food needs to be on a screen type tray that is elevated enough so the warm air can get through. And also, the food should not be exposed to the sun so a piece of cardboard sticking up in front of the top screen would stop the sun from getting to the food through the screen.
If you want something more permanent then take a look at this one.
This can be found here http://www.geopathfinder.com/9473.html?*session*id*key*=*session*id*val*
It is much more permanent, you could even leave it outdoors all year. But, it is also much more expensive and complicated to make. I may try the cardboard one first to see how it works.