How do you make rain that actually makes puddles

I want to make this ultra realistic simulation of a rain scene. Where when it rains the rain that fell turns in to water when it touches a certain mesh and when it touches the landscape. So when it falls touches for example and touches the roof of the house it will turn into like a water splash then turn to water. I know how much resources this will use but unjust want to try it out. But I have a concept too. The brain will be some actor and when it touches a mesh or landscape it will play an animation which will be a rain drop splashing then after the animation is done its properties will turn into water.
I am not expecting to find answers for this but if you can it would be nice and I have no experience in ue4 c++ and blueprinting what so ever. And animating.