Most of the meshes/textures are already there.
You do realize it's illegal to use any resources produced by a company for one of their games don't you? While you might be able to base a mod on that idea and get away with it, you certainly wouldn't be able to use their artwork. Especially on the scale you're suggesting. You'd pretty much need to do the whole thing from scratch, and then not have it look too much like the original game. Otherwise you might put alot of work into it only to be served with a cease and desist order, depending on how strict the company who made the original game is about that sort of thing. Bethesda won't even allow modders to use resources from their own games in a mod made for another one of their own titles. There was a group who ported assets from Morrowind into the Oblivion engine, and they were ordered to stop development on it, and weren't allowed to post their mod anywhere online.