Instead of buying a $500-1500 all in one unit i would like build my own. I need to be able to take temperature, humidity, PPM/TDS/EC, pH and light readings. I then would like to control AC fans, ect. based on current temperatures. I was looking into using X10 modules to control the AC part. I have found instructions on how to build each individual componet but I would like to know how to hook them all into the controller or what i would need to make this all possible.
it seems like a complex project. I would advice splitting the project in smaller ones.
Look for sensors that you want to use ( for example for temperature i advice maxim ds18b20, light reading - photocell - these are the easiest)
As for X10 - ther's a library http://www.arduino.cc/en/Tutorial/X10
Design the system on paper - the logical blocks etc and then we can think more about it :)
I wouls also advise a splitting of tasks. I would also recommend looking at something like RS485 for communication between multiple arduino units.