Calculating materials

[eandg]

We've an effective total roof area of 200m2 and another 170m2 of timber cladding. Any ready reckoners or formulas for working out how many 25mm battens I need (counterbattened to 50mm) on standard centres?

[JohnMo]

I looked at my drawings and counted, then looked at lengths I had to span. Did some adding up.  15 min job.

 

[SimonD]

You'll need to know the gauge for the roof tiles, assuming that's what you're using as roof finish.