the original cyan housing my N9 came with was horrible. Ill fitting with a large 1mm gap between the lower part of the screen and the housing. The physical buttons rattled and the whole thing creaked and groaned every time i used it. I swapped the housing out for a white one I bought on ebay for about £40 and it fits like a glove. The white is as brilliant as any lumia ive seen and is a joy to hold.

my Lumia 800 (black, direct from Nokia) has an awful screen that appears to have a seam running right down the middle of it. The light reflects in a horrible way and i was so concerned that i took it to a care point as i thought it might be a weakness that would later cause the screen to crack. The guy said it was fine, so i live with it.

in short, build quality varies so much i dont believe you can put it down to something as simple as "lumias are built better than N9 or vice versa".