In message , fred
writes
On Monday, August 22, 2016 at 6:50:30 PM UTC+1, Tim Lamb wrote:
If you are ever likely to stand on it, 4x2 would be ample.

Two other thoughts... at 5 deg. pitch rainwater is likely to wick up
under the roof and may miss a gutter. Deforming the drip point slightly
with strong pliers can solve this.

The other issue is condensation, particularly if moist air is trapped in
your shed. It usually trickles down the underside and drips off at the
purlins. Trapping a layer of dry air next to the steel can be a cure.

The 'shed' is really somewhere to keep a couple of small trailers out
of the elements. It will back up to, but not join an existing shed. No
gutters as it is on the side of a ditch. THe sides will likely be left
open or have 2 x 1s vertically at 1" spacing a la some farm sheds

You'll be fine:-)

Farm Yorkshire boarding is normally 4"x1" with 1" spacing. Keeps out
more driven rain than you might expect.

--
Tim Lamb