You need to specify the wattage or amperage of the solendoids and also it its 12v DC or AC.
That will determine whats needed to drive them; 12 Transitors, Mosfets or Relays etc.
Do you want to buy a ready made driver board, or build your own ?
Also you are also talking about 24 inputs and outputs, not to mention any display etc. so that means you will probably have to use the Mega board.
A smaller board like the Uno could be used but would need extra things like port expanders.
As you can see you need to give more thought / detail to your design needs.
Sorry for the incomplete infos, the valves are 2-way NC valves, 12V DC with 1.8 watt of power consumption. If there is a ready made driver board... it will be perfect!
I already have an Arduino UNO, i need to buy all the other things needed. Thanks for the reply
You have a working solenoid driver. You want 11 more. Its that simple. Yes you might need a
bigger power supply to power them all, but you don't suddenly need something different. If you
bought 12 footballs you wouldn't also need a tennis racket either!!
Great news, then! thanks! Of course if i can find an already made board i'll buy it instead of making one by myself.