I've made one years ago. It consists of a plywood box and 3 main compartments. The heat source is nine 75watt lightbulbs , there is a small fan which blows over the bulbs. A hot water thermostat is rigged up so the lights go out when the temperature is reached. The trays are made of wood. It works well. The only problem is the box weighs about 50 lbs so you don't want to move it around. Not sure where the plans are from.

If you live in a sunny area then you might want to look at solar food dryers.