How to make objects snap on a grid with a raycast?

hey there,

given info you provided and since you are already able to place objects you basically just have to round the positions to your grid.

you can use this following function to convert a random position to a snapped grid position:

 public Vector3 getPositionOnGrid(Vector3 pos)
     {
         float gridsize = 5f;
         var tmpY = pos.y;
         pos = pos / gridsize;
         return new Vector3(Mathf.Floor(pos.x) + 0.5f , tmpY, Mathf.Floor(pos.z)+ 0.5f)* gridsize;
     }

This should give you the center of the grid tile of this tho given Vector in the x-z axis keeping its original y coordinate.

Note that this is not tested.