You need to provide detail, e.g. house size, current roof design, some house are small but the design of roof are so complicated it take lots of works, and lots of material too. Look at Subang SS18, SS19, and USJ all so many fancy fancy roof design, but is practically useless in term of space planning.

What type of roof the contractor supply? Full glossy clay roof? or Cement roof, or maybe one layer of shin paint on the cement roof?

Truss material use? Aluminum or Wood truss? how thick the Aluminum if use aluminum truss, can it support heavy load like solar?

Wood still have its benefit comparing to aluminum truss. It handle higher load too. Some contractor use good quality "pressure treated wood" no need to worry of termite attack.