BRC isn't a good idea. Hardly renovators will use this. BRC rust when it comes in contact with moisture. And above the ceiling, there will be plenty due to heat and rain in Malaysia.

There is steel mesh which is rustproof. There are those meshes which are hot-dip galvanized used in highway dividers and security fencing. Steel mesh is practical, you do not have to remove all the roof tiles..


Normally, the other method would be to install additional  2"x2" timber batters assuming yours is made of timber roof truss. If it uses metal truss, then your battens will be made of Zincalume material. It basically adds on in between the existing batter, which means narrowing the gap that a human cannot go through just by lifting up the roof tiles.

You would need a lot of battens at close spacing and labour cost would be expensive.

Zinc (galvanized iron to be exact) sheet is good - for security, waterproofing and insulation. Only thing is,  you need to remove all the roof tiles to fix it.

Somehow, I feel adding Zinc sheets makes troubleshooting a leak harder. As you know, where you see the water may not be the location it leaks from. Adding any sheets for that matter, whether Zinc sheet or Sisalation makes it so hard to find the leakage.

How much are the rust proof Steel Mesh per square meter/foot roughly? Good for me to know as well ...