I've been playing around in Wings - making this greebled city block. Fairly happy with it, but I'll probably do a few more different ones - just for variety. My problem is when I come to apply mats to it. I can use the basic Bryce city lights/city maps... kinds of mats, but what is there for floors, city tarmac, roof tiles - stuff like that? Does any one know of any good roofing, pavement, ground stuff, sources?

look up lemog on google. the first result should be the one you're looking for. teh guy has some pretty good textures. also animax.it :)

make that http://www.animax.it/animax/Textures.htm

as a failed citybuilder..;) One thing with Wings models, is that if you're going for detail, set the materials to 'object cubic'..though if you have too much detail, Bryce will cave in.
The trick seems to be how much detail is conveyed by the material you're using. Some of the stock materials (in Wild and Fun, or Miscellaneous) set a sense of scale by window sizes, etc.
Something I do is to set material colors in Wings, then use them in Bryce to apply different mats for things like support, windows, etc. Just highlight the glass surfaces and set them to a given color, the foundations another, etc., then use the ctrl+mouse click in Bryce to experiment with various textures.
Go through Freebies for materials sites. Some good places to go are Pixel Wonder, Lunariad, Wolfies' Den (is that still around? Good planets there), Ukko (comes and goes, every few months it has the 'USS Derelict' mat, which can be good), Mascara del Poser (sp?), Bryce and More, Fallen City, 3d Commune, Puss Reboots, Tony Lynch (all the wood that's good..;), Grafik 3d Portal, Jaded Images, Bryce Alive, Cheeseworks, Why Not 3 points, etc. If you want, IM me with an email addy (I'm forgetful..;) and I can just can the whole query into a text file with all the URLS. Good luck