Mmmmn,
I think you might find that you get what you pay for with poultry housing even though some of the handmade ones do seem expensive. The auction at Murton sells similar types of timber housing at the farm machinery sales but I dont know what prices they fetch or wether the people who make them do one which really will accomodate 40 birds.
Im asuming that they would free range as the size of the run which would comfortably house 40 birds would cost quite a sum in wood and netting. On that basis a cheap option could be to buy a tongue and grove shed from somewhere like garden buildings direct and fit the perches and nest boxes yourself.
Buffy