I wouldn't call wood here cheap, but stone is,free even, odd world init...
Darren, I need a number for your supplier
we've just ordered 100 square yards and it's £65 + VAT per yard + delivery
................ free sounds soooooo much better
As for roof slates, size of latts depends upon the span, 4"x2" at 16" centres with purlins at about 1.5m (5'-0") sounds fine, Bernd, the codes over here take into account average snow load of between 2 to 3 feet with allowances for drifting and build up in valleys etc. As for joist centres 16" was the standard for many years using 1
1/
2" x
3/
4" tiling battens and
3/
8" thick plasterboard for the ceilings; during the 80's (I think ............ could have been the 70's) the joist centres were allowed to be increased up to 24" (600mm), obviously this meant an increase in joist size for traditional roof construction but very much suited trussed rafters ................ the bane of anyone who carries out loft conversions
............. the other requirements are 2" x 1" tiling battens and 1/2" plasterboard beneath (that's 25mm x 50mm battens and 12.5mm plasterboard for those not stuck in the 60's with me)
hth
CC