m2 of a roof to measure secant

I would measure the height within the loft - then the overall width - parallel to the roof slope - multiply that by 50% - then use Pythagorus' theory to work out the roof slope length. You can then determine the roof surface by multiplying by the overall length - parallel to the ridge.

Easy method (on a Mono pitch roof) would be measure the slope distance internally and the width parallel to eaves, multiply them together and add 10% for the eaves overhang.

The Scant being H/A so unless you know the angle then I believe you will not be able too. Use Pythagoras' theory to work out the roof slope length. You can then determine the roof surface by multiplying by the overall length - parallel to the ridge.

To work out the area of the roof you will need to know the height, width and length and diagonal length. In order to calculate the diagonal you will need to use the square root on a calc. Therefore if the height of the roof is 3m and the width 6m and the length 8m you will need to use the formula below: (h)=Height, (w)= half width, (c)=diagonal length, (l) length, therefore if (h) = 3m, (w) = 6m, (l) = 8m h² + w²(half width) = c² (3x3) + (3x3) = 18√ (x square root) = 4.24 4.24 x 8m = 33.9 x 2 = 67.84m² (TOTAL ROOF AREA)