The "Shack Flat Roof" piece from the Shack building set currently allows rains to visually pass through it. It doesn't actually allow rain; for example stations don't show "Soggy" underneath but the rain appears to fall through.
This also seems to be true for a brief moment when one passes under the 'seam' of two shack roof tiles in general but stops quickly once one is under a non-flat roof.
