Hey there. My name is Sebastian and i will give you some tips on how to do some really good looking buildings. First i will start by saying:
"It is only your imagination that limits what you can build"
Of cause that sentence is not completely true, but nearly.
When building, you have to imaginate big.
Well, lets say you want to make a castle. So where to start?
Lets start by asking this question: how does a castle look like? Well it got walls. But how do those walls look like? It got small pillars to protect from arrows. Then you build those. You can also walk inside the walls, then you make them hollow. But then it is like we are inside a building, so we add a nice floor. Maybe we could add some shooting windows too?. Just keep thinking like this, then you will get a lot of details pretty easy.
Also a good thing is to re-use the same detail more than once. Also even combinate stuff from other buildings on your building.
Every time you build something, its a good idea to look at it from different direction and see if it looks good. Since, if you don't, it is not sure that you can fix the mistakes later. And then you just wasted a lot of time.
Use a lot of different materials. A castle might normally be built by stone, but there are different kind of stone, and even wool that would fit, so it look like stone. Wool is a really nice material, since it can be all those different colors, which help a lot when building. It can be used for nearly anything.
A good thing to keep in mind when building is that people got texture packs, and you might even use 1 yourself, so the buildings will not look the same for the different players. Because of that, i would suggest to build with no texture packs.
Keep buildings realistic is a good thing. Make pillars that looks like they are carrying the building. Dont make flying houses, except if they have something that could do so they could fly (imagination, like obsidian is a special stone, and it could have some sort of powers) i know this sounds pretty weird, but it do work.
Don't try to build stuff from the real world i would say, since you will just mess up. Its better to make your own stuff, since then no one can compare them to the real world.
Build big stuff, it will impress a lot more, than a small house.
Use the time you need on the buildings, even if its a whole week.
When building a town or a city a good thing to do is to place the plots first, to make the roads look good.
More will come later on.