For this watering (I will add more things, such as ventilation when i finish) system you will need:
-Depends on your design, you mainly need one tube with an end sealed with holes through the tubes to let water to the sprinkler.
-Sprinklers, such as these, or you can buy small clear plastic tubes and cut little holes to make this project more DIY-er (http://www.homedepot.com/h_d1/N-5yc1v/R-100128340/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
-One per Tray to control watering and reporting humidity
-One 'Main' Arduino that other arduinos report to
-One Arduino to control how much water is in the water container and to refill it
In total you need about 10 arduinos, or if you are able to simplify the code and make it usable in less Arduinos please do. I know this might get a little expensive but It leaves you with limitless posibilities in expansion.
-Cables (20mts or more) Or get some of that phone wire it works great in these projects.
-4 pressure sensors
-Servos (one per tray)
-Hot glue & hot glue gun
-Nails (2 per tray)
-LEDs (red, green, yellow)
-A valve for each tray to water (http://www.homedepot.com/h_d1/N-5yc1v/R-100183126/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
) this picture is just for reference, you could probably find something.
-Pipe glue (or whatever its really called) It will help you make this stronger
-Wood or an structure to hold the water container
I think this is it, I will probably revise this to include all the other materials, Lets get on the building