@Odec, the decra tiles use less timber, the saving is however taken up by the expensive tiles. Fixing requires an expert, mine took about 8 days about a month ago, I would suggest you enter into a labour contract with the fundi and negotiate to have the cealing timber done too at the same time, it will save you alot, i went for this too. Once they are done, do not pay the full amount untill you are sure rain water does not leak through