This is an excellent way to deal with 3 point perspective in Inkscape

and an excellent tutorial, it should be easy to follow
I think you should create a screenshot of this tut so it can be published on inkscape.org. Although the new version is coming out soon this tut seems to fall under 0.46 features so it would probably be put under 0.46 screenshots.
Just a couple of notes; under 5. you have a typo "frong", the text is a bit hard to read but I guess you can increase the size on the screenshot, maybe give it some more line-height.