Can you provide more detail on what this spray rack looks like? Chances are there are no specific guides on how do design this type structure, and its' just a matter of estimating "spray" loads and using ASCE-7 loads and load combinations.
ASTM E1105 gives the criteria for the spray rack. We typically build ours on a grid spacing for the spray heads of 18" square or 24" square. You must then check to see that you are getting the required flow and coverage based on the standard.
For a "quickie" spray rack, you can use lawn sprinkler heads (small shrub sprayers). If you are going to do a lot of testing, get brass or stainless steel nozzles instead of the sprinkler heads.
