I'm pretty sure that this was drawn by hand on paper. That being said, there aren't any tuts on this that I'm aware of - this isometric/architectural style is hard unless you know how to do it. All you need is simple practice in doing it...and lots of it as this is very technical. Draw it at least twice the size you want, if not 4 times bigger. Me, I would do it up in SketchUp then import the lines into Gimp then color it. It's time-consuming but it'll get you pretty close. We have a lot of information on isometric stuff here but no reals tuts to match this style.