How much woodwork for a roof?

[TicklyT]

I am considering making up a 'flat' (pent?) roof, about 3.6 Metres square, something like a small car port, covered with corrugated polycarbonate and adjoining our shed.

What sort of dimensions of timber work do you think I will need to support a roof of that sort of size?

Would four purlins at, say, 100 X 35 or thereabouts spaced at 120cm suffice, or do you think the whole thing needs to be a bit beefier?

 

[big-all]

i am assuming you mean 3.6m in each direction and attached at the top to a wall

your corrigated needs support every 2ft or so accross the corrigations with something like 2x2" from side to side

then to support that back to front somthing like 4x2" every 4ft attached to a bit of 7x2" at the bottom edge with a 4x4" post each corner

or if you can have a central post you could have 3 3x3" posts with 5x2" accross the bottom

 

[TicklyT]

Thanks Big-all, That does sound a bit meatier than my original thoughts.
I can easily install 4 posts on two opposite sides.
I think I could replace the 7X2 with something quite a bit lighter, as each 4X2 can be fixed to it's own 3X3 post at each end , so the posts will just need to be tied together instead of needing a beam to support any intermediate 4X2s.

For appearances I woulld like to keep the depth of the structure as slim as I can. Would you lay the 2X2s across the top the 4X2s, 'halve' them into the 4X2s or fit short lengths between the 4X2s?

 

[big-all]

yes the 2 inch goes on top simplicity makes an easy job

if your happy with a post every 3 foot top and bottom then go for 3x2" back to front

do NOT be tempted to just have just one lot of wood back to front at the joins
without cross bits as the plastic will be unsuported and sound like thunder when the wind blows

and to keep the front and back edges simple use 6x1 treated and screw onto the face edge of the posts and with your plastic overlapping by 2" that allows you to attach guttering to the facia