Hmmmm. I suppose that it's already technically possible by making an event at the entrance of your building and several plugin commands in a row (depending on the shape of the building) to set to a transparency of 0 the tiles outside of your building. (0 will make them invisible and the plain black background will appear, unless you have a parralax background).
But, that would be tedious to do if you have a very irregular shape and that could also cause a fps lost depending on the size of the area you will want to hide.
That's a good suggestion and I will think about how implement it as a new optionnal feature, so it will be a lot more easier to do it. Thanks. :)