HELP! Newbie. What sensor should I use?

Hello. I'm a newbie here and someone recommended me this site. Please someone help me. I really need help in my project.

Well, the title is "Solar powered automated irrigation system using Water sprinkler for small plantation."

We're planning to set time for the water sprinkle to work everyday. We've decided to add some sensor which can detect raindrop in case it rains so that we can stop the sprinkler from releasing water in case that its going to rain during the appointed time.

Please, can you guys suggest sensor as well as module that will work for this?

The discussion we've recieved from our school is only about the basic coding, like timer. So, I find it hard doing this.

Thankyou for helping me. I really appriciate every little information. :)

A very simple rain detector can be made from stripboard, connecting alternate strips to form an interleaving finger pattern.
Raindrops bridge adjacent strips and hopefully your rainwater is sufficiently impure to conduct a tiny current.