 Hmm, I'm curious. Usually, people consider a through-the wall installation to be more unsightly than through the roof. Can you share some pictures of the outside (or drawings, if the building's not there yet) so we get a better idea of what you're dealing with? You don't need to have a "chimney box" visible from the outside, it would just be a pipe sticking up through the roof with flashing around it. I assume this is a rubber roof? 