More purlins, more ply, keeping the rain off?!

A great weekend, thankfully dry, spent with lovely members of the former Nautia housing co-op who came along to lend a hand. Floor joists were fitted at the north end allowing us to lay out sheets of ply to form a safe working platform at either end. The remaining purlins were raised into place and secured - almost at the end of the big-section timber jobs. So really satisfying and definitely getting a feel for the spaces. Now the big question is one of prioritisation in terms of weather proofing - whether to consolidate what we've done so far, or to crack on with the roof. I want to avoid the ply getting wet, especially on the outside where moisture could get trapped by the foil faced insulation that'll go on next...