Thanx you so much for your answers

Take a look at those two (marvelous) games :

http://www.sonicteam.com/rez/e/visuals/index.html
http://www.capcom.co.jp/killer7/english.html

Actually, I want to mix the wireframe rendering of REZ, with the solid style of KILLER 7 (concerning the landscape, I don't think they use cell shading), to build a huge town. I was hoping doing it without any textures, to gain precious memory space as the visuals are quite simple (cubes and lines) affording me to increase the numbers of different buildings (but maybe I'm completly wrong)

The wireframe rendering is not appropriate as you can see the surfaces that normally should be hidden. I already thought about your method Dusty3D, but it adds polygons (but it seems to be the best solution anyway)

I've been searching on google for days to see if there's a solution, without any success. I'm beginning to think the only solution is to use some polygons to draw the edges and coloring them, like you said.

But thanx alot anyway