Refer to old articles of aluminium roofing sheets, they come in rolls of average of 600mm to 1300mm depends on the manufacture and specifications. As stated in previous articles, the aluminium sheets comes in rolls at the factory just like toilet rolls but with different widths and thickness based on specifications.
Calculating the roof required could be done by calculating the surface area in square meters of the area covered by the aluminium and for some companies it could be calculated in meter lengths ,knowing the width which is 600mm above as constant.
For a simple gable roof as shown in pic 1 with length of 25.2m. First you must know the height of roof from the section.
For this sample we are taken the eight to be 3meters (10 feet)to know the length of leaf “x” or “y”
Remember the pythagoras theorem
Hence the area of roof is (6.8 i.e x)+6.8 i.e y) multiply by length 25.2m=342.72m2
If the width of the roof comes in 600mm or 0.6m, the length of the roof require will be 342.72/0.6m
=571.2 meters length
So for some companies they could give their quotations in meter length so just ask for the width of the rols and follow steps above.
For a complex roof like pic 3 above, then you can opt to do a fast estimate based on the linear area covered as shown by roof plan as it may be a bit complex and difficult, so you can divide the roof plan to sections of rectangles or squares as it may applies –(four right angles). Then add the areas together and add 10% of the same area, because the higher the roof, the more the plates , and the more complex the roof the higher the numbers of offcuts which will also increase the numbers of aluminium /plates required . So for pic 3 ,add areas of rectangles A,B,C and D which is the big center.
i.e (8.2m x 1.2m)+(1.2mx8.2m)+(1.2mx8.2m)+(22.8mx12.2m)=311.28m2
Now for a more accurate and scientific calculation, you must know the height of the roof , have the basic knowledge of calculating area of a triangle which is ½ base x height . And Pythagoras theorem to know the side of any triangle . Also remember the area for a rectangle is simply length multiplied by breadth.
Assuming the height of roof is 3meters as as previous in fig. 2, and taken the major part D as a simple gable roof (check the different sections on plan fig 3) and ignoring the hipped or bevelled section.
So area of roof as previous is ( 6.8m+6.8m) multiply by length 22.8m=310m2
Add areas A,B,C
+310m2 +9.84m2 +13.44m2 + 9.84m2
With your estimate is also the RIDGE and GUTTERS.
Ridge is the roof material you use that will cover and seal up the points where two leaves of your aluminium sheets meet to protect the interior from rain, it usually overlaps the two adjacent leaves of roofing sheets .
And gutter is usually underneath, it gathers rainfall and help to channel it to wherever deem fits according to design. Is at the taper ends of two adjacent leaves of aluminium sheets to collect water.
The difference between gutter and ridge . While the ridge is up protecting rain water the gutter is down collecting rain water and channeling to some drains.