you can probably find some materials on the interwebs somewhere, but it's easier to make your own materials from downloaded textures. try
www.cgtextures.com - they've got a fairly good selection, or just try search in Google images for a particular texture - e.g search for 'brick texture' under the images search and you should get hundreds. you'll need to learn a bit about texture mapping and material creation unless you know this already...? are you intending to render the 3D model with textures? and if so, do you intend to render in ArchiCAD or will you use another render package such ads Artlantis?
