Is possible to get the roughness of a material by line trace?

Hi, I am trying to get the value of roughnees of a material but the object is vertex painted. I want to know if its possible to get the vertex color or the material roughness by using a line trace by object. Its hard because if I get the value I used to add roughness its always the same all over the object, but I need to get the change I make with vertex paint for puddles.
I just want to add different particles to run over puddles and sounds maybe but I dont want to use a simple mesh over every puddle I paint for detect collision.
Thanks a lot and sorry about my english.