So, I just finished my first megaproject. It is an obsidian castle with double walls. In the center, there is an obsidian tower to the top of the map which my nobles live in. The quality of the rooms improves with height, and at the very top of the tower is a statue garden. Additionally, there is a smaller tower at each of the corners of the castle, each of which is dedicated to one of the four elements. The fire tower is filled with magma, the water tower with water, the earth tower with natural obsidian, and the air tower is empty. The entrance consists of a drawbridge on the west wall.
Constructing this thing first consisted of leveling out the building site, as I embarked in a mountainous area so I could have a volcano, sand, and clay. Fire clay made meeting noble room requirements much easier, and I managed to pack royal rooms into a 5x5 space inside the tower, and the sand allowed me to use windows as boundaries for the room. The volcano also meant that I had 2 natural obsidian layers, which made attaining enough stone rather easy. The only actual challenge was moving the magma into the towers, which wasn't too hard due the nearby volcano and the ability to make the pumps out of glass. There is no deathtrap or doomsday device in this castle, because it was built on an island and there would be nothing to use it on.
Also, does anybody know of a good visualizer? I'd like to see this in 3D.