For you to make a quality environment art piece for your portfolio, you're going to need an overall concept for the scene, a unifying painting (or two). This is why we use concept art in game development. This list of individual texture choices isn't going to cut it, because your env will end up looking like a hodge-podge,…
Take a good look at the Env Concept Artists thread for inspiration. Just don't grab one of their pieces and recreate it in 3D, unless you ask for permission first, and clearly label your work as inspired from so-and-so's concept. Also I just saw Marc-Antoine Hamelin's portfolio (Marcan here on the boards). Really beautiful…