On Thursday, 23 July 2020 11:44:40 UTC+1, Andrew wrote:
On 23/07/2020 09:51, wrote:

I am building a lean to in the UK
Length 27' x death 8' x height 8' with a slope for the roof upto 10'
I am considering using 2" x 4" for all the Framing with 16" between each uprights.
Again for the rafters I was thinking of using the same wood 2" x 4" at 9' lengths to allow for some overhang.
Does anyone have any concerns or suggestions


really depends on the weight of the roof covering. Will it be
tiled with artificial slate or marley concrete tiles or something
lightweight like epdm ? . You might have to go up to 6x2 for the
rafters.

The manufacturers of whatever hard roofing you choose should have
tables on their website showing the amount of overlap neeed for
your 12? degree pitch. There are limited tile choices for a
pitch that low, eg


https://www.jjroofingsupplies.co.uk/...umpitch_ln=567

though there are ways round those limits to some extent.