I have thought of building something like that but I was under the impression that shadecloth alone has too-large holes in it, and you need to use something finer. It will probably work just for the reason that the individual spaces are large and if you stuff a few plants in there they will shield each other.
Like someone else said take seed stock pods from the inner pods if possible, and if you absolutely want to guarrantee the purity of the seed individually cover flowers with a fine material. Use fans to move them if the wind doesn't or get in there and gently shake them when the flowers open, or touch the stems near the flower with an electric toothbrush to shake the pollen free.