Now that's delayed gratification!

Buildings like those took decades to make because all labour was by hand, and all material transport was by horse and cart on poor roads.

Their safety record was poor because no-one thought much about buidling-site safety generally then. Also, because structural engineering was purely empirical and the nature of materials not really understood, collapses of buildings under construction were not unknown.

Sometimes failures during building were due to builders skimping on the foundations or other parts - this still happens in some parts of the world today. I think that was more common with private projects like the huge fortified homes of Mediaeval times, than with churches.

Modern equivalents in scale, though in very different styles and materials, would take a tenth of the time to build. The new Coventry Cathedral in modern style took only a few years in the 1950s to build, alongside the stabilised ruins of the Mediaeval one that had been destroyed in a WW2 air-raid.

The safety rules and equipment are far tighter now, too, though the regulations vary from country to country. For example, scaffolding has to be erected to proper standards including with hand-rails and toe-boards, and on major works at least, subject to passing independent inspection before being signed off for use.

Some cathedrals still show signs of the building methods. At Salisbury there are some small, square holes in the external wall. These were "put-logs" to support the cross-members of the Mediaeval, timber scaffolding made from rough-hewn wood: the word survives as "putlog" for the spar itself. The builders had forgotten to plug the holes afterwards. While the cathedral's famous spire still contains the timber framework that was its temporary support during construction!