I have a small budget (about $1000) to build a rain-out shelter over a raised bed (4 x 10 m) in an experimental garden. Ideally, it could open and close based on weather conditions (I will use a Davis weather station).
I have not built or used a rain-out shelter in my own research but some folks in my lab have. See pages 12 and 14 of this thesis: http://www.tru.ca/__shared/assets/McCulloch_Thesis_201333095.pdf. More recently, they built much larger wood shelters but I don;t know the exact design.