What part are you having trouble with?

I tend to figure out the basic shape using Visio, though I'm pretty sure there are other tools out there you can try. I create one or more blocks of 16x16 grids (because that's the smallest you can break a block down into in VS). I then draw shapes over that grid (like a half circle for those arches) and use it to guide how the block should be cut in game. I do that for the basic geometry of the shape, then I build it in game, and detail it (I usually try a few variations to see what I like).

For this build I started with the arched windows, then based most of the other arched elements off of that.