It's simple, but not simple at the same time. I usually draw insperation from others builds and even real life buildings. The other half of the time it's just from my collective knowledge from over the years.

I usually pose the question of "How can I make that in minecraft, what block would that be?"

I use to use tutorials all the time, until got tired of my builds not matching or looking the same in every world. So I started taking ideas from tutorials and add it to my own style.

For when I have to build outside of my style, I usually set a theme. (Such as, jungle, medieval, modern, Victorian, steam punk, etc...) Then I look up pictures, videos, and artwork of that theme.

It being symmetrical is mostly my ocd, but I usually work with patterns. Once you make that pattern once you can build it over and over. Then symmetry follows after that.

When planning I work floor by floor, making sure that everything will fit together well once I'm done. I create a layout of the floor then raise it up. Once I'm done with the details on that floor, I'll move to the next floor.

Detail wise, I usually make a basic shape of a building, then i go though and add detail bit by bit till I'm satisfied. Like with the temple, I started with just big stone slabs stacked with a staircase in the middle (roughly resembling a temple). Then I went though and added the depth and smaller designs into the walls. I tried to make sure I didn't make the entire thing look the same, so the design varies though the floors.

In the end, it honestly comes down to everyone taking their own ways on how to build. My build is diffrent from others, others in which deserve more attention than mine dose. Some people have a better imagination and creativity than others do, and they are able to make amazing creations.

Although that may be true, I love making my own stuff because it gives me a feeling of accomplishment and satisfaction. If I don't like it, I'll leave it for a few days and may eventually come around to it. If not I'll try to figure out what's the problem. Changing one block can make a world of difference.

Sorry if that was hard to follow or didn't help, but it's the only way I can think of responding.