In this post in describing how I built my first solar dehydrator in Portugal. This was done in Quinta dos Sete Nomes, which is a lovely and lively co-op eco farm in Sintra. Building it took me in total a full week. To build one you need basic woodworking skills and tools.
The concept is very simple: To build an insulated box that heats up air with direct sunlight. Air starts moving up and by convection dries up everything that is laid inside. The box is perforated from the bottom and top part to circulate the air. Temperature doesn’t really need to get over 60° Celsius (140F), so that keeps things simple.