Roofing Sheets only 10ft long, how many do I need?

[barbapapa]

I want to convert a flat roof to a hipped roof. The building is 45 ft x 50 ft. I happen to already have 50 roofing sheets which are 10 ft x 3ft and it makes sense to use these. I would like to calculate how many more I need. The building is overseas and If I dont ship more the 50 I already have will go to waste. (only different profiles are available on the island)
Im already shipping some other materials so the cost of the container is not a factor.

Can someone please give me a calculation so that I can work out how many more sheets I need. I know you will ask me about pitch and this can be set at any degree. I know hipped is more complicated than standard pitch with a gable but this building is subjected to hurricane winds which will remove gable ends like a pack of cards. In addition any overhang will be minimal. I will not be doing this work but I am trying to ensure I have enough materials to make the 50 sheets I already own are put to good use.

Any help would be greatly appreciated.

 

[Roofer]

If you assume no overhang your building size is 13.8 x 15.3 metres

If you pitch at 20 degrees across the narrow side then the rafter length will be about 7.3 metres giving a roof area of 2 x 15.3 x 7.3 = 224 sq metres

If your sheets are assumed to be 3 metres x .9 metres and laid with a headlap of 200mm and a sidelap of 150mm this would give a coverage of 2.8 x .75 = 2.1 sq metres per sheet.

Divide 224 by 2.1 = 107 sheets. An allowance must be made for cutting to hips and breakage - say 23 - that means 130 sheets.

You also need about 42 metres of ridge and hip cappings plus allowance for cutting and waste