Oh we have some pretty big
cathedrals here in the UK, I live just a 30 minute train ride from two of them in Liverpool. The Anglican cathedral is a behemoth of a building, it's frequently cited as being the most massive free-standing building in Europe, and it's easy to understand why when you get up close and personal with it. Chances are this is one of the few buildings on the planet that could survive a direct hit from a Hiroshima-sized atomic bomb. It's the world's fifth largest cathedral, the bell tower is 331 feet tall, and building it completely exhausted the local sandstone quarries. It also boasts the UK's largest pipe organ. There's something like 60,000 tons of rock in that building, and it's not only about the size of a battleship, it would cost as much as a battleship to rebuild it if it ever came tumbling down. Another of the "mine's bigger than yours" statistics centres on the peal of bells -the highest working peal of bells in the world, and the heaviest in the world ... hopefully held in place securely, because the last thing you want is 31½ tons of bells crashing down on you from 220 feet up ...
A short way up the road is the Roman Catholic cathedral, nicknamed "Paddy's Wigwam" because of its interesting shape. Originally, the architect Sir Edward Lutyens designed a massive piece of one-upmanship that would have made the Vatican look impoverished, but the cost of building that proved too much even for Liverpool, a city with a history of paying for architectural extravagance on a colossal scale. The alternative, present day design was not without its own problems, being something of an architectural adventure, and it quickly developed a reputation for being a high-maintenance building until alterations were made in the 1990s. It's built on top of the only surviving part of Lutyens' original design, the crypt, which, hilariously, plays host each year to the Liverpool Beer Festival, something I imagine would
never happen in a fundie megachurch.
Whilst entertaining this tangential diversion, anyone wanting to attend the 2014 Liverpool Beer Festival can find out more
here.
As for capacity, I reckon both buildings could house around 5,000 people each, though the Roman Catholic cathedral is a little cramped if you fill it with that many people. The Anglican cathedral, on the other hand, is so enormous that you could probably fit a medium sized aircraft carrier inside it, and consequently probably qualifies as a 'megachurch' on the basis of mass and volume alone.