Took me about two days to finish it up. Not in a row, of course. I took breaks.
Basically I started with a 25x25 smoothstone flat area. Then I did all the fence posts you can see that go around the structure, then I did the roof that goes on top. Repeat for each floor. I did that the first day, then I did the interiors this morning, I literally just finished it.
There's quite a bit to the interior, which I might get some screenshots of if you guys want to see a nice tour of each floor.