Hi Medi, The controller I'd like to build could do either a small hydro grow or a grow room. I've found lots of open source (OS) projects and commercially available products but the OS projects are under developed and most don't seem to be going anywhere and the available products start at $1,300+ without the modular devices the controller needs to run. I'd like to build a $300-$400 controller and offer modular components that you add depending on what growing technique you use.
Sounds like a great idea, and at a great price point. An Rpi would make a great controller or one of the newer boards like a HummingBoard or for that matter, the Beaglebone which has a ton of places to plug in sensors. Just food for thought, but best of luck with the project!!