I get the idea of perspective but that tutorial is messed up. I messaged the back line of the roof going down on the undetailed picture and the detailed picture and they are not the same angel or the same length of line in the back. The undetailed is much shorter and the angel is such that it makes the slant more pronounced and it looks distorted to me. Where as measuring the detailed one it is has better perspective.
Explanation of the measurements on the bottom of the tutorial will be very helpful to me and I thank you so much for researching this.
No they aren't the same angle but that is the beauty of it..it's showing you how the perspective lines work. That where you place your lines makes a difference in how the house turns out. Where (and how wide) you put that vertical (corner) line makes a huge difference in how the house looks and from what perspective you are looking at. As does where you put the end line (the line that determines how long or short you want the house to look). You can make your house look however you want.
The more detailed version looks so different because it is set apart from the horizontal line. The less detailed version is sitting along
the horizontal line (as illustrated). The same technique is used for the more detailed version however it is set below
the horizontal line. You use that horizontal line and vanishing points as a guide to help you no matter where on the page you decide to put your house.
Did I help or completely muddle things up?
I don't recall ever having to do exact measurements. We made our ruler do the work for us. but we didn't sit and measure and measure and measure. We made a straight line..figured out where we wanted our vanishing point (or points) and worked out from there.
See if this is any better for you. The house in this example is set above
the horizon line. As you can see the same method is used for it as the house along the horizon line as the house below the horizon line.