good Idea but not very feasible. The variety of systems out there using different modifiers would make it hard to code in probably and if you are suggesting only for a specific system then that goes against what roll20 is about. All roll20 does is replicate the table that people gather around to game. Does your table automatically adjust your dice rolls for terrain? I know mine is just made of wood that the family sits around to eat dinner when there isn't a game on it. All the features that roll20 has now is enhancements to help us use it easier and the developers have repeatedly stated that they want to keep roll20 system agonistic which just means they are not willing to put in code for one specific system. Anything they code in has to be usable across many game systems. I do like the idea of the terrain modifier but to my eyes and thinking I don't think it is feasible but I could be wrong. On the other hand I think there is work in the api scripts that could do what you are suggesting.
