If you allow me I think aluminium roof is still the best over others. Infact advantages in aluminium far outweighs Nigerite products. It is very light, it can span any distance, it doesn't add too much weight on the structure, ease of transportation,e.t.c
I had written an article on it's advantages before, check:
thirdeye, pls can u give me an estimate of hw much it will cost to build a 5 bedroom bungalow in a sloppy ground in anambra state. i was advised by someone to do german floor on it, and that there wont be any need to level the ground but to build acoording to the shape of the land. my email is emyworld2002@yahoo.com