flat roof advice needed

i am building a shed, well rather a garage.
it is built out of 4" concrete solids

the size is 25'W x 16'D
i am wanting to put a flat roof on it so that i can stay under the 3Mtr height.

how many roof timbers will i need and at what spacings should i put them, i am covering the foof with 8' x 4' 18mm sheets

also, what pitch/slope should i put on the roof

thanks for any help you can give me with this



Martine

you could span the 16' with 225mm x 50mm timbers set at 400mm centres.

you will need solid bridging at mid-span and at the joist ends if not built-in.

use regular furring or diminishing strips to create falls. these can be bought at most builders merchants. they provide a fall of approximately 1:80.