You probably need a roofing contractor. If you want to DIY, you'll need to figure out where, exactly, the leak is coming from, and then search for videos on how to repair that specific part of the roof and go from there. So, you'll have to go into your attic when it's raining and find the trickle. Identify the component that isn't working (for example- a chimney flashing, a pipe flashing, etc.) and then ask. No one is going to magically know which of the hundred things that could be wrong you are dealing with.
Or maybe it is a related question and you want a laser that can rapid-fire shoot down rain droplets before they hit your house?
You're going to want to buy 20 laser diodes to set up in a 10x10 grid on your ceiling. Then hook up sensors that are triggered when something passes through the beam. That way the next time it rains you will be able to see the exact place on your coordinate grid that the water is coming through, so you know what part of the roof to patch up Use more diodes for higher accuracy