how to get all the face of a model not visible to outside.

hi everyone,

i have couple of architectural model that are too heavy for my purpose.i am thinking about deleting all internal wall and inside face of the if i set around 36 to 48 point and check if any of that point is not visible from the any one of face vertex,i delete it.
am i in the right direction or there is a better way of doing it? please share your wisdom.
and if you can point out which maxscript command i should look for.