"£Do you get much unskilled labour on a building site?"
Compared to what?
Hod carriers, mixers, general labourers, tea lads, all need certain skills, but how would compare them with sparks, carpenters, plumbers.. all of whom come with training and certification (nowadays)
"Then as now - unskilled meant unemployed."
Fair enough, but you mentioned highly skilled labour, masters and guilds, which is what I was responding to.
"There is much more to see in a church or cathedral than just the building"
o there isn,t, basically you go in to look at the architecture (unless they have the odd Caravaggio hanging on the wall)
"and the services are the reason they exist."
Nine people out of ten have rejected general use of the ordinary church, and those people who use Cathedrals and Abbeys for worship are miniscule, and quite often confined to the elite.
As Musket says, you don't need an elaborate, cold draughty damp and often neglected building to worship, anywhere will do.
When one local church was renovated years ago, the faithful went to mass in the pub (Gleesoms, for anybody who knows this area).      
As god is supposed to be everywhere, you don't need a building at all.
Jim Carroll