I can remember the "quick(??)" build of my former Kingdumb Hell. The foundation was prepared months ahead, including pouring the slab. Fact is, the witlesses made such a big deal out of a stupid slab of concrete--as if the filthy angels were there (which would actually be all the more reason to NOT visit the stupid slab. More than anything, there is nothing to gain from looking at a slab of concrete that is to be a Kingdumb Hell in a few months.
And, the workmanship is pxxx poor in most cases. It is usually possible for anyone to get a frame of that size up in a weekend, especially when you have an adequate crew. But, when they use inferior materials, you get things like fires, bad climate control (and most of them are known for unreliable air conditioners and/or heaters), and things falling apart within a few months of constructing them. They can get the finest wood for their boxes (out of your donations), but if they are poorly assembled, usually they end up looking sloppy or functioning poorly.
Beyond this, the Kingdumb Hell wasn't even 100% finished when we moved in. Curtains, blinds, and window dressings were not even installed. They had to redo the window dressings between the main auditorium and the second school/back room. In fact, they ended up using a blanket for a time--taped to the frame (and were embarrassed when, during the book study in the back room, the tape gave way and they were exposed). It must have been another 3 months before it was completed--and, as late as 8 years in, they had an ongoing heat problem not fixed.