Do you remember those structure spawners in creative? Very useful, aren't they? Now imagine if they were available in SURVIVAL. It would open so many opportunities for grie- I mean, building!
Alright, I made that joke about griefing, but I'm going to do best to make sure it can't be used for trolling purposes.
Basically, every faction would have a new mob, the Builder. The builder would sell structure spawners, but only spawners of its faction. Since people would obviously use these for low-priced materials, they would be VERY expensive. Prices would range depending on structure size.
As for the griefing, I'm thinking that structure blocks would only be able to be used in previously bannered areas. It would be unable to be placed if the blocks of the structure overlapped the banner, and would also need a certain amount of empty space, so you can't build a pyramid in a small cave, or right next to another structure. Like the structure blocks in vanilla, there would be an outline of the structure the first time you try to use it, and the second use would spawn the structure.
This idea seems very strict and risky in function, so if there are any major problems with it that you can find a solution for, I'd welcome it.